Good luck with your new female bettas, I'm sure it will all work out fine.
Bettas are pretty much surface feeders. I used to keep pygmy corys with one of my male bettas and I found that he would eat his own pellets and freeze dried bloodworms from the surface and would also nibble at some of the corys sinking granules while they were at the surface and after they started to sink he wouldn't chase after it. Corys are bottom feeders, so they used to ignore pretty much anything unless it actually hit the bottom anyway.
If your other fish are mainly middle feeders like most small tropicals are, they will wait for most of the stuff to sink before feeding, although some may also feed from the surface too - they may take some of your bettas pellets from the surface but probably not everything and certainly not if your bettas get there first!
I think it's a bit of pick and mix when it comes to feeding community tanks, it generally works out OK and each fish type gets it's fair share. I would try to feed them seperately by feeding one food type and the then the other at the different side of the tank or at different times. Best of luck with it