1 - If there is a dispute as to whose dominant was played first, then the player responding to their own action gets priority.
2 - If there is NOT dispute as to whose dominant was played first, then the first dominant gets priority.
If it was clear whose dominant hit the table first, then the player who played first gets their dominant to activate and complete first.
If there was a dispute as to which dominant was played first, player 4 and player 3 are not considered the same player since teammates in teams are never considered to be the same player under the current rules.
Since the land of bondage is shared in teams, player 4 could have given half even though player 3 fought the battle and would be responding to his own action. However, if player 3 gave half, player 4 was not responding to his own action. You didn't say which player gave the half.
If I was the judge though, I would give it to player 4 since his team was making the same move that would get it in a type-1 2-player game. Give half and bury it.
I don't think that there is an official rule when neither player is responding to their own action. Since it would be nice for it to be clear and ruled the same everywhere, I'd be in favor of ammending rule one above for teams to something like "the player OR TEAM responding to their own action gets priority."
Now, that just leaves what to do in multi or booster when neither player is responding to their own action?
Mike