Well, the two have been added out of quarantine yesterday and now I REALLY can't tell if either of the newer two are actually females or have been playing me for a fool this entire time. But at this point, I give up, they can figure themselves out.
I've been watching them closely and there's been some flaring and chasing, but nothing excessive. In fact there's been points where all four were in close proximity and tolerating each other's presence (albeit in a passive-aggressive manner). And even if they do get orney with each other there's 125 gallons worth of space to escape in and multiple caves/otherwise secluded areas to hide away. I think we're finally all good here.