Salt and pepper? I take it one is a peppered city and the other albino? That doesn't work, cories need to shoal with cories of the same species. The only cories that can be kept all together that are part of the same family are green/emerald, bronze, and albino. Your cories need members of their own family, so sad to say you will have to get rid of one and get the remaining one at least 3 more of the same type. That is if you don't have the same family of cories.
Also is your substrate sand or gravel? Cories need sand as the burrow their nose in the sand to find food, also gravel can injury their barbels.
Your Betta may be too aggressive for tank mates. It is something to look at when deciding tank mates.
15 Gallon NPT
1g no tech bowl in the making