Samuel Vimes, the Librarian, and Death.
The Librarian would revolutionize the field of looking after books, an honour beyond honours. Death would be a welcome sight posthumously, especially if one could reincarnate and meet him several times. Sam Vimes is exactly the sort of incorruptible and cunning street copper you'd need to fight inequality and shake up any peacekeeping forces, though admittedly he'd need a bit of luck here and there.
As for visiting: The Librarian and Death I'd absolutely visit for, say, tea. Although the Librarian prefers people who don't wear out books by reading them, at least we'd have the same interests, and it'd be fascinating to learn the ways of apehood. Death combines pleasant civility with morbid philosophy, which would at least make for some curious discussion. Vimes... probably not, if I'm honest. Awesome and morally strong though he is, he's also a workaholic. I doubt he'd be remotely interested in any casual time outside of police work, much less make a good conversationalist.
As for where they'd live: Neighbours would be fine for all of them. Might be tricky in Death's case, being an anthropomorphic personification outside of space-time. And I suppose one could get used to the assassins climbing over one's roof to try (and fail) to kill Vimes while he's shaving.
As for family: Don't see why not, though probably not Vimes'. Nothing against him, mind, but he'd have plenty of enemies looking for ways to get back at him, in which case being a blood relative would make one a target. But Death seems like he'd be a pretty decent if odd relative (give or take what that'd mean in the real world). I don't think it'd make much difference to the Librarian, since apehood is more important and more congenial to him.
I think that should answer all your questions, Mixa.