The Dumbledore story seems to indicate that he was capable of holding his own with his brother and Grindelwald in a duel.
Could this old pub landlord have beaten Voldemort 1v1?
harry potter - Why did Albus Dumbledore hide the identity of Aberforth Dumbledore? - Science Fiction & Fantasy Stack Exchange
harry potter - Did the Dumbledore family line end with Albus and Aberforth Dumbledore? - Science Fiction & Fantasy Stack Exchange
Voldemort has a twin brother?
Oooo, or his twin is a Squib. He loves Tom because they're brothers but Tom grew to resent him as he fell more into the Dark Arts and pureblood propaganda in Slytherin house. After Tom creates the first horcrux, he sees his brother as no better than a muggle and a disappointment to the Slytherin bloodline. Tom tries to kill him in the aftermath of his horcrux madness. His brother goes into hiding. London is a big city and there's so many muggles that it's fairly easy to dissappear. He moves often but he doesn't know for sure if Tom is even looking for him anymore.
He does get himself a subscription to the Daily Prophet though. He knows that Tom is going to be something amazing one day, and if he can't be there by his side he still wants to read about it happening. Though the rest of the Wizarding World is in the dark about the identity of the rising Lord Voldemort, Tom's brother isn't. He recognizes the cruel intelligence behind every move the new Dark Lord makes. His brother is terrible, yes, but great.
When a baby is hailed in the papers for killing his brother, he never expects to stumble across them in his own muggle neighborhood. He's not quite sure what compels him to take the child. Perhaps it is comraderie among the few who have survived Tom Riddle's direct attacks.
Although he's a Saint compared to a Dark Lord, one could hardly say he's lived a good life. He, too, has a disregard for the law and an arrogant streak that often gets him in trouble. But kidnapping is beyond his usual operations and he's almost sixty, far too old to be raising a toddler.
And yet. There's a green-eyed menace in his living room frantically pretending that they didn't just knock over his golf clubs.
Well.
Tom can just come find them both then.
In the meantime, he'd better find something that Tom wants more than he wants their deaths.
(A philosopher's stone, dun dun dunnnnnn)
More on reddit.comI have discovered something about the Dumbledore siblings names!
Videos
(Harry and Doge discussing Dumbledore during Bill and Fleur's wedding):
'I saw the obituary you wrote for the Daily Prophet,' said Harry. 'I didn't realise you knew Professor Dumbledore so well.'
'As well as anyone,' said Doge, dabbing his eyes with a napkin. 'Certainly I knew him longest, if you don't count Aberforth - and somehow, people never do seem to count Aberforth.'
Harry Potter and the Deathly Hallows - p.127 - Bloomsbury - Chapter 8, The Wedding
(The Life and Lies of Albus Dumledore):
'He were a headcase, that Aberforth,' says Enid Smeek, whose family lived on the outskirts of Godric's Hollow at that time. 'Ran wild. 'Course, with his mum and dad gone, you'd have felt sorry for him, only he kept chucking goat dung at my head. I don't think Albus was fussed about him, I never saw them together anyway.'
...
'Aberforth blamed Albus, you know, as people will under these dreadful circumstances. But Aberforth always talked a little madly, poor boy.'
Harry Potter and the Deathly Hallows - pp.289 and 292 - Bloomsbury - Chapter 18, The Life and Lies of Albus Dumledore
(Doge on Aberforth in his obituary):
Three years after we had started at Hogwarts Albus's brother, Aberforth, arrived at school. They were not alike; Aberforth was never bookish and, unlike Albus, preferred to settle arguments by duelling rather than through reasoned discussion.
Harry Potter and the Deathly Hallows - p.22 - Bloomsbury - Chapter 2, In Memoriam
(Dumbledore to Harry at King's Cross):
'And then ... you know what happened. Reality returned, in the form of my rough, unlettered, and infinitely more admirable brother.'
Harry Potter and the Deathly Hallows - p.574 - Bloomsbury - Chapter 35, King's Cross
I think the answer is simple. No one cared about Aberforth, no one was interested, no one asked him about the uninteresting, unsuccessful, uncouth, unintelligent goat botherer. Who's gonna ask Albus Dumbledore, in interview, about his unglamorous brother, when they could be talking about the twelve uses of dragon's blood, or the hot political topic of the day, or his latest decision as Chief Warlock of the Wizengamot?
Obviously this is entirely unfair on Aberforth, but I think that was one of JKR's points. The answer is simple: nobody cared. Which turned out to be quite helpful with the Order and then, later, after Dumbledore's death. Aberforth, unnoticed, could have the mirror and look after Harry in Hogsmeade and all of that. And I think, partly, Dumbledore might have been quite happy about that and that might have contributed to his not bringing Aberforth up - especially to Harry. And, obviously, after Ariana, I think it's pretty obvious why Aberforth wouldn't have wanted to define himself as Dumbledore's brother and wouldn't have paraded the fact, and so he went pretty well unnoticed.
Albus didn't divulge that the barman of the Hog's Head was Aberforth, but he didn't deny it either.
We do know Aberforth was in the Order of the Phoenix so they must have had a later cordial relationship, and Moody at least knew he was Dumbledore's brother.
The little people in the photograph jostled among themselves and those hidden right at the back appeared at the forefront of the picture. ‘That’s Dumbledore’s brother Aberforth, only time I ever met him, strange bloke … that’s Dorcas Meadowes, Voldemort killed her personally … Sirius, when he still had short hair … and … there you go, thought that would interest you!’
Harry Potter and The Order of the Phoenix | Chapter 9: The Woes of Mrs Weasley
He also never hid the fact he had a sister, he just wasn't asked.
Harry, in Harry Potter and the Deathly Hallows, comes to the realisation that in all his meetings with Dumbledore he never once asked him about himself and his family, and as we only see Dumbledore through the eyes of the Harry we don't get to learn his past.
Aberforth blamed Albus for the death of their sister. That's why they fell out.
You have asked for quotes from the book which have never actually addressed it, but in the film Fantastic Beasts: The Crimes of Grindelwald (written by J.K Rowling) it's confirmed that Credence Barebone is actually Aurelius Dumbledore.
In around 1901, Aberforth had a son, Aurelius Dumbledore with a girl that he fell in love with in Godric's Hollow. However, the girl was "sent away," presumably by her parents, either before or after Credence's birth, although Albus was aware of rumours that there was a child. Due to the strained relationship between the Dumbledore brothers, Aberforth neither confided in nor sought Albus' help. Aurelius was eventually sent away to America with an aunt, where he was adopted by Mary Lou Barebone and given a new name, Credence Barebone.
In 1932, Credence attacked Albus and accused him of abandoning him, revealing to Albus that he was supposedly a member of the Dumbledore family. During a duel between the two, Credence's phoenix spread ashes on his body and Albus realised that Credence really was a Dumbledore and that he was actually Aberforth's long-lost son. However, by this point, Credence was dying due to his nature as an Obscurial slowly poisoning him, something that Albus sadly recognised from his experiences with Ariana. After foiling Grindelwald's plans at the walk of the Qilin, Credence, in poor health, accepted his father's offer to come home with him.
Dumbledore Family Tree
So no, Albus and Aberforth were not the last Dumbledores. There was at least one other.
In the books, it’s easiest to infer that the Dumbledore line ended with Albus and Aberforth.
I think it is also difficult to say that the Dumbledores were an ancient wizarding family. After all, Percival married a Muggle-born so he can’t have been very pureblood leaning. If the extended Dumbledore family was, it is most likely they became extinct in the male line other than Percival.
Book 7, which is heavy on Dumbledore lore, speaks as if Albus’s nuclear family was the only Dumbledore family. We pretty much know Albus didn’t have kids so that’s the end of that line. As for Aberforth, I don’t think he’s the type to go around getting girls pregnant. Especially since it’s implied in the books he was a goatfu- uh, he preferred to devote his life on research and experiment on goats. I think from his lifestyle, he was probably asexual but that’s just me assuming.
In the FB movies, Aberforth has a kid so I guess that’s not the end of the line. I don’t know if Credence dies tho cuz I deleted those movies from my head. Nothing in those movies counts as canon information, even if Jo wrote it. Seeing as she changed McGonagall’s age by thirty to fifty years.