Eponymuse, I think I covered that with the word 'vengeance.'

Those coincidences are otherwise satisfied by the fact that Bones' motives are served by Narcissa's Immolation, whoever did it. Given what we know about her, she'd act the same way if Dumbledore or Moody were Narcissa's Immolator. Still, it does make some narrative sense for her be the one.

I am not at all confident that Aberforth was involved. I would like it very much, though, if someone could add something more to or take something away from the rickety scaffold propping this theory up.

Aberforth may have died just to emphasize the harshness of the war in ways the source did not. If that's the case, I'm making a red herring out of a pointless bit of the set. However, there was nothing in the text that tells us that Aberforth was a tragic casualty of a meaningless war or anything of the sort. For now he looks, to me, like a gun on the mantle.