Is there a large closet or bathroom within the master bedroom? If so, I would send the family in there while I stood watch over the locked bedroom door. Consider giving a loud verbal warning that you have called the cops and whoever it is should leave immediately. At the first sign of trying to enter the bedroom, I would open fire. While a bedroom door may not be much cover, it is a good "line in the sand" that I can dare anyone to cross.
Of course there might not be sufficient time to sequester the family in one room. In that event, I would try to have everyone take cover where they are. If everyone is upstairs, then defense of the stairs is probably the best tactic.