i'm trying out a low intelligence run so I can't join them, my only guess so far is to just kill the guys at the entrance, which wilkl take a while and a bit of save scumming and I'm not sure if I can even pick up their power armor

Killing random Brotherhood paladin won't work since there is no correlation between external appearance of NPC and thier inventory. Guards just have this specific sprite and their parameters boosted but posess no PA item at all. In fact all Brotherhood paladiтs who appear to wear a PA won't work as a loot source. ) OFC I'm speaking about the vanilla game, some mods could alter the situation.
AFAIR, there are two option to get the PA in the Fallout. Both are quest-triggered and both are in the lower bunker of the Brotherhood. So, you are at least to get a permission to enter that bunker anyway.

Join a caravan going to the brotherhood of steel, that will get you in the bunker. With a high repair skill, you can get power armor after you get an part for it.