+1 to what Doggy said.
Male+Female(s) Splendens in the same tank without a divider=Chaos. It is inevitable that, in the end, you will be left with one severely beaten up betta or none at all.
A 10 gallon is a nice size for a simple betta however, or can can even be divided in half with a betta on each side, but make sure the divider is super secure so that they can't get to one another.
Bala sharks get GIGANTIC by the way, and like schools I think. You'd probably need some sort of huge, heated, indoor pond to keep them properly....