snails v.s. mollies....v.s. bettas?

[Spencerjunie]

my mollies are disappearing. I have gone from 5 to1 mollies in my 10 gallon. in my 10 gallon a week ago I had 2 mollies, 1 beta, and 2 suckerfish. recently, one of my 2 mollies disappeared. I found a molly carcass(just like bones) on the bottom of my 10 gallon and my snails were eating it. 2 days before that molly died my beta disappeared without a trace. who has been killing my fish?????? snails or suckerfish?!?!

[Crowntails]

Mollies shouldn't live in 10 gallons. They need a minimum of 20 gallons and the tank that is brackish. What are these "sucker fish" that's not a species name. Are they plecos or otos or what? I think the betta killed them, bettas and mollies don't mix well.