Durbkat.........silver tipped sharks and ballas are very different. balas are actually of the minnow family while the silver tipped are of the catfish family.
anyway these guys get quite big which limits what can go in the tank. i belive somewhere close to 2 feet. also with out knowing what type of gouramis we cant help much, they could be dwarf which are only 12 inches or a kissing which is a foot.........and there are even larger gouramis out there. also the same for the molly depending on the type they range in size from 2-5 inches. i will be glad to help i just need to know what type of gouramis he has and the type of molly and then i need to find out how big the silver tip will grow to.