I would do a few pwc
's over the week and use Epsom Salts.
Did you do the Epsom Salt treatment before when all this was going on initially?
What is the water temp?
As for the snails, you might put them into a different container for awhile. And take care of the Betta with whatever he needs to heal.
You could try starting with (aquarium) salt dips.
And add the Epsom Salt therapy, and see if it looks like it will heal after a couple days. If it looks worse, then doing medication with him in a seperate container and add back in the snails to the main tank. And gradually with water changes the ES will be removed.
I would get the IAL into the tank though to help him out.
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