i have an idea.

Throw a party together

Osu sucks. Everyone is so determined to be better than everyone else that they spread rumors and try to sabatoge other chapters. Sae wanted an annex close to their chapter house so the move made sense. Delt is getting their chapter house redone so they could need a place for step kids. Because it's considered university housing they can't party there. Sae has a different property since the house is split and have no university restrictions. If delt drinks there they'll be in trouble with the university. If sae throws a party nothing will happen. Therefore a joint event probably won't happen there unless it's on the sae side and with all the drama already I don't see the two having good relations.