in this case I would doubt you would have planed on having to defend your self from a relative while you are out for Dinner
I doubt you ever plan on having to defend yourself most places.
I would expect these folks knew there were "hard feelings" between them and the murderer and as soon as he started getting angry, my hand would have been on my weapon, and drawn if that could be done under cover.
The probably had more foreknowledge of the impending attack than they would have of a random shooting in the same place.