I wouldn't recommend shell-dwellers in a 5 gallon. If you're considering Tanganyikan cichlid shell-dwellers they are really quite aggressive and are prone to bullies so one may well muscle in on the other and chase it to death.

You'd be ok with one betta.

Or some endlers.

Or micro-rasbora...a little school of them would look cool with some plants and a few small branches?

Would love to see some photos when you decide what to get.