This sounds EXACTLY like my three. Zeke is the oldest.. and has been with J the longest. Then Bunny, and then Eli. Bunny and Eli LOVE each other... I mean LOVE each other.. we find them making out sometimes... But Zeke just tolerates Eli. They dont play at all. They pretty much ignore each other. Zeke has snapped and went after E several times. We always step in and roll them and all that.. and then we're good for another month or so. Eli and Bunny love to play.. and Eli plays rough.. I have always thought for the same reasons as you said, not much socialization as a young puppy, taken away from mom early (he was a sickly puppy), etc... So I think he plays rougher than he should and he steps all over us and the other two, like he doesnt know better. But Bunny will take it all in and she yips when she's had enough. Or she will sit down and put both paws on his neck (resembles a hug) and starts licking his face. That usually ends it as well.

Best advice I can give... is to just watch them. We dont trust the three alone together.. B and E are crated together (large crate, dont worry) and Z is by himself. When we're home, we watch them constantly. Zeke has warning signs before he snaps. Eyes change, Ears perk up, tail goes straight up and still... Im sure it also has to do with the puppy stage... Zeke is 5/6ish and Bunny is 3/4ish and Eli is just over 1 year old.. so theres a big difference from Z and E, and I think that has a lot to do with it.

Good luck! Im sure Falise will learn to accept Celeste and the fact that she is there. Zeke has done so with Eli.. and we got him in May I believe.