I have a 20 gallon tank filled with about 16.6 gallons. It's separated between my male and female bettas. The tank's so large and it feels like a waste of space, so i wanted to get them a couple tank mates. I'm currently working at a pet shop where they have mollys and a dwarf gourami for sale and i wanted to buy 2 mollys to put with my girl, Caboose, and the gourami to put with my boy, Tex. Is this too much for my tank? or would it be okay?