In the future once they're healed I'd get more of the knitting(?) material that you made the dividers out of and silicone a couple sheets together(to make one big sheet) and then cut it do size so that you can place it above all two dividers in the tank. Hard to explain but you might understand what I'm attempting to describe.
I hope your bettas heal, poor babies.
yes it makes sense. I'm just going to push for individual small tanks for each one. there is an ebay sale for sponge filters for 1$ and 1.50$ shipping. So i'll snag a few of those and then each betta has his own home