If both the Radiers and Chargers move to LA, one of them is going to have to leave the division and swap places with a team in the NFC West. The Raiders have one of the most thuggish fan base in all of football. It's so bad that they don't play the 49'ers in preseason anymore due to concerns about security. One could imagine what it would be like if the Raiders and a local rival they were having to share their stadium with met twice a year, perhaps 3 times if they met in the playoffs. They'd have to dig a moat around the playing field and fill it with crocodiles. One of those teams almost certainly would have to leave the AFC West as well as leave the conference.
Since the Seahawks were the only team to be forced to move in the last realignment, my guess is that they'd give us an option, move to the AFC West or stay put. Personally, I'd love to go back to the AFC West and resume our rivalry with the Broncos and Chiefs, two teams with enthusiastic fan bases, and as one poster mentioned, become the first and only team to win both an AFC and an NFC Championship.
I can't see 3 teams moving to LA. For one, the league has already said that they will only assist financially with one stadium plan. Right now, St. Louis is ahead of both Oakland and San Diego in their stadium efforts and recently won a victory in that they do not need to put their stadium plan to a public vote, so it looks like either the Raiders and/or Chargers will be moving, and it could happen as early as next year with a new stadium ready by 2019.