OK, again I will play referee. We are waiting for clarification on what happened in the OP. We aren't sure if the BU killed the ball and they decide to call the BR out for interference, or on the throw to first. In the former the runners return, in the latter they stay where they are.
I always stress to new umpires and coaches both to sit and read rule 2.00. It is the basis of all of the rules and rulings. Without having this knowledge it causes all kinds of arguments and ejections.