Five Bettas or five fish altogether?
The problem is, Cories should be kept in groups and with three Bettas already in the tank, theres not enough room to keep a group of Cories unless you can find Pygmy Cories which stay under an inch. Algae eaters are the same way, most Plecos grow too large for a 10g. Otos stay small but again, they should be kept in a group.
I'd go with about a dozen Ghost Shrimp and three females. Everyone has enough room and your not overstocked.