What I like about you, is that you pointed out you know you've done wrong and want to fix it :)
Right now, put her in a 1 gallon quarantine, with daily water changes (with tap water conditioner added). It will probably be a fungal infection which will be worse in 80 degrees anyways.
As for the others, remove the male from the females. It can be really risky, especially since you know he is a meanie.
Even DECOR needs to be taken care of
Otherwise it is no longer decor, it is a dust collector. Anything that has a heart, a mind, a soul... Breathes, or serves a purpose in the world - whether plant or animal, we need to take care of. We've taken away mother nature, therefore we must become it.
It is not that hard to care for bettas... It may seem like it through all the reading, but you can make it easier on yourself.
Try rehoming the females, and for the sick ones you can try, or you can euthanize. Keep the male and we can easily walk you through everything you need to make sure he remains healthy.
A healthy betta will have better colors, finnage, and attitude with a little bit of proper care
That way he can still be a "look at me!" fish, but still have good husbandry behind that.