Whee! I feel *smart* now. Aberforth, yes. I see him being much more informed and involved than the books had room (or inclination) to show; after all, older adults are even lower on the JKR list of characters-I'm-interested-in than Marauder-era adults. (Although they don't seem to have been as completely exterminated, LOL.)
Petunia! OMG. Brilliant. Fascinating! This --
How Snape "turned to Petunia to figure out how to live as a Muggle again. She might have even helped him in exchange for helping her stay out of anything wizarding."
-- is an awesome prompt! Are you thinking about writing it? Either way, I think it needs to be promoted as a kick-ass bunny-starter. I've always wondered what happened in the Evans family to make Lily so saintly, so Mary-Sue perfect, and Petunia so bitterly hateful to Harry. Perhaps Snape wasn't the Marauders' only victim, nor the only person Lily failed to stand up for. Between Lily and her set, and - let's face it, Snape, who can't have been a very congenial youngster - Petunia can't have had any better impression of Wizards than the most rabid purebloods had of Muggles. Her encounters with the WW during Harry's school years wouldn't have immediately helped.
But clearly, somewhere by or during DH she's seen more of them, and that may have changed her mind. Enough to ally with Snape for such a reason as you suggest?
My. What an interesting concept!
*chuckles*
Snape would certainly be, of all in wizardom, the one least likely to be affected by Petunia's barbed tongue and spite. The one most likely to return it in kind, too. I suppose their conversations might be quite the exchange!