I know what you mean , i have 10 bettas and all of them in their own tanks for the same reason. And i even try to use different changing cup ,when i change them. I have names on the cups.
Also 3 females to put together kind of dangerous number any way.
Yes I have several new Bettas. Each one is in their own tanks. I'm afraid if I put the females together, another disease will spread to every one and die. So far I have 4 Male Bettas and 3 Female Bettas. Thank you for your concern :)