I really enjoyed this. Aberforth is such an intriguing character, and you've definitely captured how I see him. He's unsentimental and so acutely aware of Albus's manipulation, but the connection between them is something he can't disentangle from. Not that he's been trying very hard -- he could presumably choose get as far away from Albus as possible, and yet here he is in Hogsmeade, as close as he can get. Even though he doesn't appear, Albus is very present in this story, always the puppetmaster.
The relationship between Aberforth and Sirius is wonderful and completely believable. I think you got Sirius's character to a T. Aberforth is an astute observer of him and how he's changed over the years, he sees straight through the cocky exterior and sees what Sirius has lost, and what he needs.
"Everything is getting strange, like it was then. Part of me wants to take Harry and run. It's what I should have done fifteen years ago. Taken James, Lily and gone. If –"
For some reason this really strikes me, I'm not sure I've heard it articulated quite so clearly before. Sirius is perpetually stuck in past regrets -- and how could he not be? For him everything seems to be playing out just as it did before, and it makes sense that he would want to go a different road this time, yet he sticks by Albus instead. It's fascinating to think about what would have happened if Sirius really had taken Harry and run, but I don't know if Sirius could. He wants to trust Albus so badly.