Sounds like a pretty tough situation. Either your son can just deal with it or talk to the RA and try to move. If he ends up staying, I think he should feel free to clear space in the common room as needed, and toss junk into corners. IMHO people who make huge messes aren’t too picky about where exactly their mess is. “Hey my mess was in that corner and you moved it into that other corner!” - that’s probably not a complaint he’s going to get.
It definitely sounds like he should simply write-off the rommates and seek friends elsewhere. Since he’s into sports he should have no problem finding guys to play pickup basketball and other such things. That’s usually just as simple as walking over to the nearest game and asking if he can get in. Or he can even just find a nearby empty court and start shooting hoops solo, and eventually somebody will come along to join in. There are probably tons of other guys in the dorms into similar things for him to hang out with and I suspect once he gets over the rommate thing, he’ll be more than fine.