A large adult Oscar of a foot long or more, 2+lbs can make a 125 look small all by itself. Adding 3 other fish that can reach 10 ins would constitute an overstock imo. A regular JD can be **** for the other considerations, and an EB is far too delicate. A single tolerant Oscar, and a Sev that can stand up for itself may work out. Never any guarantees. Fyi, Oscar lives alone just fine, and if you can grow a really big one in a proper setting, with optimum care, you will have a fine water pet for maybe 15yrs. For a mixed tank at 125g, I would skip the Oscar.