Sorry for the late reply. I'm in the Pacific Standard time zone and I spent the morning doing water changes. >.< Something we're all familiar with . . .
All right. First, I agree with Myates. For Murick, discontinue the salt. If he's healthy, then the salt may actually do more harm than good.
For Fin, continue with the salt. How many days do you have left with the Fungus Cure treatment and does it seem to be helping him? If you have only a day or two left OR it does seem to be helping, continue with it. Otherwise, stop the Fungus Cure for Fin.
The problem with saprolegnia is that its symptoms look a lot like the symptoms for columnaris too but the treatment is different for each disease. The best thing you can do for Tia is continue the Fungus Cure in case it saprolegnia AND continue with the salt in case it is columnaris.
Be sure to keep Chloe separated from the others. I believe she may have lymphocystis, which is contagious. Discontinue the Fungus Cure and salt for her and just keep her water super duper clean.
For Tamera, it sounds like she may have developed columnaris. 3 tsps of aquarium salt and lower temps of about 76 degrees for 14 days, along with clean water.
I do believe that once all of your girls are healthy, you can put them back in the 10g, provided you buy at least one more girl so you have 4 betta girls in there. Make sure there are lots of plants (fake or live) and hiding holes for the girls.
For the boys, they can go in a divided 5g but a 2.5g divided is probably too small.
I don't have any experience with snails but I do think most people remove them when treating with salt. If they're anything like land snails, they might a little sensitive to salt.
For all of your fish in small containers, it's really important to do 100% daily water changes. I know it's a bit of work but with 5-6 cups of water, the ammonia builds up pretty fast. One way to make this easier is to get a 1 gallon jug such as the kind spring water or milk comes in. Fill with 1 gallon of dechlorinated water and 1-3 tsps of salt (depending on which fish you are treating). Let the salt dissolve. Now you can use the premade water for easy water changes.
I hope this helps you. If you have any more questions, definitely post. I never go more than half a day without checking in so if I am unable to reply in the afteroon, I will certainly reply before the day is over (uhm, by day is over I guess I mean Pacific Standard Time).
Good luck and hang in there, I know it's a bit overwhelming right now.