if you do have to kill the brothers, just how do you guys do it short of getting a lucky nuke and invuln right before entering?
First you have to take care of the initial monsters - lucky phase is the way to go, as you already found out - but then you need to kill them all as well. Assuming you port somewhere between bruisers (still locked up) and the lost souls/cacos (trapped behind a door), this easy to do if you have INT 2 and preferably some shotgun - wait until ther are no souls too near the door, open while staying out of line of fire and cornershoot. If any lost souls threaten to get into the doorway, simply close it and wait for it to lose interest.
The probably easiest way to kill bruisers is using missile launcher, which you can get by cleaning the wall just before the anomaly (there is a thread with tips on clearing the wall somewhere right now, if youi have problems with that).
Ready your missile launcher, stand in the same line of tiles as the lowest or highest bloody part of the wall separating you from the bruisers - that way a bruiser will be directly in front of you when the wall falls. Once that happens, shoot your missiles straight in front of you until he either dies (if you are lucky with your rolls) or comes within your vision. Then run back until he gets out of sight again and repeat. The missile launcher is very precise, so you should hit frequently. You should have plenty of rockets and there is nothing you can destroy, so use that. With int 2 you can easily aim at the bruisers if they move up or down, otherwise you have to guess where they are.
If you are unlucky with the rockets, you have plenty of room to retrat. The doorways are a good place to stop and switch to cornershooting, if the bruisers cooperate and approach in such a way that it is possible without their retaliation.