I believe more than one player can ambush at the same time. I would simply resolve the ambushes in order around the table, each getting to steal one card from the set being traded in. Of course, more than one player performing an ambush will result in the ambushed player being most of the way to another set for their next turn. (And that card can only be ambushed by player colour.)
But the correct order is that it goes first the person you first call for an ambush and then the next you called....
But yes 2 persons can make an ambush.