kinda semi plot hole that all participate are strangers to eachother. If any premade group showed up they would absolutely dominate (like the MC's group for example) it would take literally ages for them to betray eachother.
groups of 3 can come to 50/50s but groups of 4 is best. put the resident just needs to keep his head down and wait it out. They win if they kill him not maintaining status quo