i hate to say it, but you probably need a bigger tank. hillstream loaches get to be about 2-4 inches, and if i'm not mistaken they prefer to live in small groups. cories definitely need to be kept in groups, or at least pairs, they're extremely species social and become stressed when kept alone. to provide the proper care, you'd need 2-5 of each species (betta excluded, of course) and that would mean housing them in at least a 20 gallon tank, possibly more since they're both bottom feeders and would therefore end up crowding each other. additionally, hillstreams generally prefer water a few degrees cooler than bettas and cories are most comfortable in, and like a strong current which is a definite no-no for bettas.