Female bettas in 20 gallon fish tank?

Yeah, like I said in your other question, the danios are really the most hardy. I've had many and I even left one accidently in the garbage can for several minutes and it is still alive today. You could get about 12 of them and 3 or 4 cory cats to pick up the food on the bottom.

Yes, your tank is a perfect size, but you could fit more than that in there. Just don't put more than one male or they will fight.

They're so beautiful

Awe, you should get like, 5 or 6 that are all different colours!!

Female bettas, unlike the males, usually get along ok. A 20gal would be more than big enough for 4 or 5 female bettas. I had 4 female bettas in a community tank that was a 20gal. long and they did just fine.