Minus the RTBS and betta you've got a little bit of room but that'll get taken up forming proper groups. I wouldn't add any other shoaling fish to the tank, either get rid of all the neons and get a group of another small shoaling fish or up the neon count.
For bottom feeders you're probably best off with either a group of corys or kuhlis rather than two small groups of each. Is your substrate sand or gravel? The kuhlis need a sandy substrate since they dig, otherwise they'll injure themselves, corys prefer sand as well but it isn't as necessary. I have a group of four kuhlis that has been very active so far, I'd say add two more at least and you should see them a lot more so long as they have plenty of hiding spots (they really have great personalities when they feel safe!)
If you want to stock your tank a little more, adding to the existing groups rather than adding completely different fish would be your best option, you'll get better dynamics in the tank.