The Weasleys are considered one of the prominent wizarding families, although their lack of money and their sympathy for non-pure-blood wizards and even Muggles makes people like the Malfoys look down on them. They live in The Burrow, a ramshackle house of four or five stories “a little way outside” the village of Ottery St. Catchpole (CS3).
For the last couple of generations, the Weasley children have all been male (Arthur, for example, is one of three brothers); Ginny Weasley, born in 1981, was the first girl to come along for quite some time (JKR). Both Molly andArthur are related to the Black family.
Molly is fiercely protective of her children, but she has her hands full; the Weasleys are, almost without exception, risk-takers who courageously give their all for what they believe in (well, perhaps the twins do it from pure joy too). From the summer of 1996 on, the Weasley family clock has all hands pointing at “mortal peril.” Molly took it around with her from room to room.
When the security of Grimmauld Place was compromised in the summer of 1997, the Weasley home became the new headquarters for the Order of the Phoenix. After Scrimgeour was killed and Death Eaters took over the Ministry, most of the Weasley family members played a role in resisting the Death Eater pogroms. Ron’s absence from Hogwarts was kept secret by using the family ghoul to fake a case of spattergroit, however, once Ron, Harry and Hermione were captured and the deception revealed, the family moved to Aunt Muriel‘s house nearby where it was safer (DH24).
The entire Weasley family fought in the Battle of Hogwarts, including Percy who had realized what a twit he had been. Molly’s worst fears were made true when Fred was killed in an explosion and later, when Bellatrix attacked Ginny. Enough was enough: Molly fiercely counterattacked and killed her psychopathic cousin before she could threaten anyone else (DH36).
Molly and Arthur have at least twelve grandchildren (DH/e, YL).
The Weasley Family Tree:
(NOTE: The date of Fred’s death is incorrect)
Family
Septimus Weasley (b. circa 1910s)
The husband of Cedrella Black (born between 1912 and 1917). Cedrella's marriage to Septimus (was he a Muggle sympathizer too?) caused her to be "blasted" from the Black Family Tree.
Although unconfirmed by Rowling, there is reasonable certainty that Septimus and Cedrella were Arthur Weasley's parents. If this is the case, Septimus could be the grandfather that gave Ron the Wizard Chess set (PS12). See my Notes, below.
Arthur Weasley (b. Feb. 6, circa 1950)
Husband of Molly Weasley. (More...)
Molly Weasley (b. Oct. 30, circa 1950)
Wife of Arthur Weasley. (More...)
Bill Weasley (b. Nov. 29, 1970)
Oldest son of Arthur and Molly, he works for Gringotts; married to Fleur Delacour, and father of Victoire, Dominique and Louis Weasley. (More...)
Charlie Weasley (b. Dec. 12, 1972)
Second son of Arthur and Molly, he works with dragons in Romania. (More...)
Percy Ignatius Weasley (b. Aug. 22, 1976)
Third son of Molly and Arthur; employed by the Ministry of Magic. Husband of Audrey Weasley, and father to Molly and Lucy Weasley (YL). (More...)
Fleur (Delacour) Weasley (b. circa 1977)
One of the four Triwizard champions; with husband Bill Weasley she had three children: Victoire, Dominique and Louis Weasley. (More...)
Fred Weasley (April 1, 1978 - May 2, 1998)
Twin with George. (More...)
George Weasley (b. Apr. 1, 1978)
Twin with Fred, husband of Angelina (Johnson) Weasley (YL). (More...)
Angelina (Johnson) Weasley (b. late October, 1977)
Gryffindor (1989- 1996) Quidditch Chaser, captain (1995 - 1996).
A tall black girl (GF16) and an excellent Quidditch player (PS11); born in October, the week before Hallowe'en (GF16). She put her name in for theTriwizard Tournament but wasn’t chosen (GF16), and went to the Yule Ball with Fred Weasley (GF22, GF23). Angelina became Quidditch captain in 1995 (OP12), which stressed her out and gave her something of a mean streak (OP13).
Later in life, Angelina married George Weasley and had two children, Fred and Roxanne (YL).
Angelina probably took the Weasley name when she married George, but this is not certain.
Wife of Percy Weasley (YL).
Hermione (Granger) Weasley (b. Sept. 19, 1979)
Best friend of Harry Potter and wife of Ron Weasley. (More...)
Hermione probably took the Weasley name when she married Ron, but this is not certain.
Ronald "Ron" Bilius Weasley (b. Mar. 1, 1980)
Sixth son of Molly and Arthur, and the best friend of Harry Potter; husband of Hermione (Granger) Weasley (DH/e). (More...)
Ginevra "Ginny" Molly Weasley (b. Aug. 11, 1981)
Seventh and youngest child of Molly and Arthur; She is the "first girl to be born into the Weasley clan for several generations." (JKR). Wife of Harry Potter (DH/e). (More...)
Victoire Weasley (b. May 2, circa 1999 or 2000)
Hogwarts c. 2011. Victoire is the daughter of Bill and Fleur Weasley. Harry’s son, James, caught Victoire snogging Teddy Lupin on Platform 9 ¾ as she was preparing to leave for what was most likely her seventh year at Hogwarts; at the time she would probably have been seventeen, and Teddy nineteen (DH/e). She was born on May 2nd, the anniversary of the victory over Voldemort (YL).
Middle child of Bill & Fleur Weasley, this name could belong to either a boy or a girl (YL).
Youngest child of Bill & Fleur Weasley (YL).
Rose Granger-Weasley (b. circa 2006)
Rose is the older of Ron and Hermione’s two children, and their only daughter. On 1 September 2017, Rose was preparing to take the Hogwarts Express to her first year at school, and was rather nervous about whether she’d be sorted into Gryffindor (DH/e).
Hugo Granger-Weasley (b. circa 2006-2009)
The younger of Ron and Hermione’s two children, Hugo seems to be good friends with Lily Potter (DH/e).
In the epilogue to Harry Potter and the Deathly Hallows which takes place September of 2017, Hugo was not yet old enough to attend Hogwarts, but instead hangs out laughing with Lily on Platform 9 ¾ while his older sister, Rose, prepares to depart for her first year at Hogwarts. Though we don’t know his exact age, Lily Potter was nine at the time, and it’s likely the two of them were within a year or so of each other’s age. This would place Hugo’s birth roughly between 2006 and 2009, and his first year at Hogwarts at circa 2019 (DH/e).
Eldest daughter of Percy & Audrey Weasley (YL).
Youngest daughter of Percy & Audrey Weasley (YL).
Eldest son of George & Angelina Weasley (YL).
Youngest daughter of George & Angelina Weasley (YL).
Other relatives:
- Arthur's two (unnamed) brothers (JKR). Is Bilius one of them?
- accountant cousin of Mrs. Weasley - a Muggle accountant who isn't spoken of by the Weasley family (PS6). He or she would actually be a Prewett relative.
- Bilius - uncle to Ron who supposedly saw a Grim and died, twenty-four hours later (PA6). Fred missed having him at Bill and Fleur's wedding, saying he always good for a laugh (DH8).
- Lancelot - Great Auntie Muriel's cousin who was a Healer at St. Mungo's (DH8). He is not a Weasley (DH4), but he may not be a Prewett either.
- Mafalda (non-canon; see commentary)
- Muriel - Molly's aunt (DH4) and Ron & Ginny's great aunt. She has a lovely "goblin-made" tiara and is apparently is a memorable kisser (HBP14, 29). Muriel is not a Weasley, but as the sister or the sister-in-law of one of Molly's parents, she may not be a Prewett either. Many thanks to Yvonne B. who pointed this out.
- Errol - aged and decrepit, Errol is a family owl. He barely survives some of his deliveries, but he's still hanging in there.
- Hermes - This owl belongs to Percy.
- Pigwidgeon - Known affectionately as "Pig," this tiny brown owl belongs to Ron (GF5).
Other canon notes and references
- Arthur was one of three brothers and had no sister. We don't know his brothers' names.
- Molly's maiden name was Prewett and she had at least 2 brothers, Gideon and Fabian. We don't know if Molly had sisters; none are ever mentioned.
- Ron (and by extension Bill, Charlie, Percy, Fred, George and Ginny) had an uncle Bilius, a great-aunt Muriel and a grandfather who played Wizard Chess. In addition to uncles Gideon and Fabian, of course.
- Ginny is the only Weasley girl for generations.
- Molly refers to a relative as "Our Great Auntie Muriel," but because she says "our," this could mean Muriel was a great aunt of Molly and Arthur, or of Ron and his siblings.
- Molly and Sirius are "cousins by marriage."
- Therefore, Molly's parents are probably closely related to the 'Ignatius Prewett' listed on the Black Family tree. If the Black Family tree Jo auctioned is complete, Ignatius and Lucretia cannot be Molly's parents themselves because they are indicated as being childless.
- Arthur is "something like" Sirius's second cousin once removed. This describes a relationship where one person's great-great grandparent is the same person as the other person's great grand-parent.
- Therefore, Septimus Weasley is Arthur's father. Septimus's children would indeed Sirius's second cousins once removed. Assuming the Black family tree Jo auctioned is complete, this relationship fits the facts and can be explained no other way.
Commentary
Notes
Mafalda, the "Weasley Cousin" (non-canon)
Rowling had created the character of a female cousin to the Weasleys for Harry Potter and the Goblet of Fire; however, that character disappeared in rewrites.
On her website, Jo gives some more insight into the character: Her name is Mafalda, she is the daughter of the nameless accountant second cousin (a Prewett cousin through Molly - PS6), and she would have been a Slytherin (JKR). Here's what Rowling has to say in an interview about Mafalda:
Q: Last time we spoke you said there'd be a Weasley cousin. It didn't appear. You've deceived me!
A: It got pulled. Sorry about that. What happened on Book Four, and one of the reasons why it was easily the most difficult to write, which had absolutely nothing to do with Harry being famous or me being famous, was that for the first time my plan fell down. I got halfway through and realised there was a huge gaping plot hole. The two ends just didn't meet. It was entirely my own fault: I should have had the sense to go through it very carefully before I started writing. So I had to do an enormous amount of unpicking and in the process I'm afraid the Weasley cousin disappeared.
Q: Will we see her again?
A: Possibly. I really like her as a character but it's quite a complex plot I'm dealing with so I'm not sure that she'll fit anywhere else. She'll be the "character that might have been." (Nr)
Guesswork (not canon):
- Bilius was one of Arthur's 2 brothers. Not canon: We don't know Bilius's surname and we don't know if Molly had more than 2 brothers. "Uncle" can also be an honorary name given to non-family members, though this doesn't seem likely.
- The grandfather who gave Ron the chess set is Septimus Weasley, Arthur's father. Not canon: We don't know his surname, so it could have been either Arthur's father Septimus, or Molly's father.
Calculating the ages of the Weasley children
There has been much confusion about the relative ages of the Weasley children. Jo cleared this up on 
her website with the definitive answer that "Bill is two years older than Charlie, who is three years older than Percy, who is two years older than Fred and George, who are two years older than Ron, who is a year older than Ginny."