I am limiting my remarks to the question presented...
I like an O/U with 00 Buck as an indoor weapon. Obviously if it’s 3 on 1 you were dead before before you began, unless you’re using a Saiga 10 streetsweeper.
I prefer and SxS with external hammers for reasons of utility but otherwise share the sentiment. I t will argue that in close quarters you aren't necessarily automatically dead in a 3:1 situation. If you catch them in a hallway, you may very well hit more than one in the same shot. If they're in different rooms, you may have time to reload. It doesn't take more than a few seconds with practice.