Pictus catfish are too cramped for a 10g. I'd suggest rehoming yours to a larger tank.
As for snails, nerite snails, mystery snails (Pomacea diffusa) and assassin snails are your best bets. Not all nerites cannot breed in FW. There are a few that can such as Vitta usnea and Theodoxus fluviatilis but the latter is harder to come by as a lot of snails in Europe are underrated and not often taken notice compared to the Asian and American species. Nerites prefer algae above anything else. You need to sustain their algae supply and make sure the tank is well established before you consider nerites. They can eat anything other than algae but that's the trickier part. I have a few friends I know who tried pea flavored snail jello to their nerites and their nerites went off to eat those so you could try that. I haven't tested it myself since I don't have time at the moment to prepare another snail jello for all my snails.
Be very careful where you get your nerites. Make sure the source has them acclimated in FW already as SW species are unlikely to survive the abrupt changes of saline waters. Keep your pH and KH high as soft acidic water tends to erode their shells badly. Nerites as well as the MTS, are also great calcium absorbers, something to consider so focus on calcium enriched foods such as snail jello (with calcium tablets such as Tums added), rehydrated seaweeds, collards and dill greens. You could shop at kensfish.com for invert sticks with 20% calcium content or simply give them a tablet of Caltrate or Tums every few days. Daily doesn't hurt if you think you like to see the snails eat them but the nerites will ignore anything mentioned completely except algae and pea flavored snail jello.
As for apple snails, be sure you are buying Pomacea diffusa, not the Pomacea canaliculata. Canas are illegal from interstate shipping and if you've been buying from other states, the USDA will make sure to track down your house and confiscate the illegal snails to be burned in an incinerator. Only legal way to obtain them is buying them within your state. Diffusas are plant friendly species and will prefer dead and decaying plant parts rather than healthy plants. All stages of life of diffusas from egg clutches to adults are now permitted to be shipped across USA without any permit requirements but do make sure the snails you get are actually diffusas. If in doubt, post your pics and I can help you from there. Diffusas reach golfball size only whereas canas reach baseball size. Guideline for diffusas is one snail per 2.5g whereas canas are better off singly in a 10g or in two.
Assassin snails are another species to consider. They do not proliferate as quickly as most snails. It can be influenced by the abundance of their food supply. Like the nerites and apple snails, assassin snails are sexual and therefore require a partner of opposite sex to be able to breed. I'm still trying to determine how best to determine their sexes as I have three mated pairs out of nine and already laid a few eggs and could not quite distinguish any differences except males do cling on the right side of the females as traditionally done by other species of snails that are sexual. A 10g could fit 15-20 of assassins but assassins are very expensive at $4 and over depending on the seller. PM me if you want some and I can direct you to a seller I know who breeds them.