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?
https://www.aquariumadvice.com/forum...py-374191.html
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.
https://www.aquariumcoop.com/blogs/a...-for-sick-fish
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.
__________________

New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?

Start here - Aquarium Advice Article
https://www.aquariumadvice.com/guide...ater-aquarium/
FW Favorites right now Clown Loaches, any shrimp - SW Vase Red Mangroves