Cross-Tribe Vote: At one point, before the merge, both tribes will be sent to tribal council. However, these tribes will not vote out someone from their tribe, but instead vote out someone from the other tribe!
In a tie vote situation, the original tribe would vote to decide who gets out. If it ties, there is no re-vote; it will go straight to rocks.
In a setting with more than two tribes, each tribe would have one other tribe decide who goes from that tribe, decided randomly.