A and B were the first generation of would-be L-successors. Mello and Near are the fourth. That means there were two other generations in between. It's unknown what happened to the second and third generation, but given what happenedto the first, it couldn't have been anything good.
Perhaps WMG, but why is Mello the one who knows about and is the narrator of these events? Well, he sure is a hell of a lot like the killer in that story, Beyond Birthday. Both he and the killer were raised at Wammy's to succeed L, are basically rivals with another successor (Near for Mello, A for Beyond) are considered inferior for whatever reason to that rival (Near was honestly the most likely to succeed L since he wasn't such an impulsive jerk, A at least died within Wammy's while Beyond ran away and became a serial killer), and do what they do to basically one-up their rival (which gets a little odd for Beyond because it's verses L and not A, but it still works). L told Mello about the LABB Murder Case and nobody else knows - this could easily have been as a lesson to Mello not to be a B.
If all of B's money is acquired through stolen bank accounts and such, why is he living in a modified warehouse instead of a real apartment? It's not like he couldn't afford it.
That'd send up red flags, though, if someone who shouldn't have such a large about of money started having and using that amount of money.
Do the Wammy's kids have some kind of world citizenship thing? He wasn't in the US long enough to apply for US citizenship, and almost certainly arrived illegally. Why was B imprisoned in California, rather than being extradited back to the UK?
Truthfully, we don't know much about B. For all we know, he could have been at least part American, and if one of his parents was American he could have duel citizenship.
Because his crimes were against American laws, not British ones. The UK had no jurisdiction.
