I said I was unsure and had all three factions allied with me at the time of the mission (I went with brotherhood in the end) but it was awesome Nobody shot me. I was just spectating the brotherhood slaughtered everyone. Eventually the railroad won because there were too many of them and the last 2 brotherhood guys didn't enter bunker hill but instead slaughtered everyone outside and then just stood there. Brotherhood killed 10 railroad guys for each one of them that died though. Synths never stood a chance