What would happen if an exiled king returned to claim his kingdom and was aided by both an exiled lord seeking to reclaim his lost lands AND the current holder of those lands? Split them down the middle, probably angering both?

That’s probably not a situation that would happen (because normally whoever got to the exiled king first would insist on the price for their support, and the other would oppose the exiled king as a result), unless you had a situation in which the exiled king was incredibly likely to win and thus everyone was trying to get on the winning team.