A few months ago, we got 2 snails and 2 hermits. The snail shells, probably about and inch or so, the crabs less than an inch. The Undulated is the only one that really messes with them. However, one of the little hermits overtook one snails shell. One snail remains, gets hasselled by the Undy every once in a while, but pretty much stays under the substrate.
We decided to get 50 hermits, Dwarf Zebra, I believe. Well the Undy went wild, but couldn't break the shells, but she has tormented them to no end, so now the crabs hide in the day and clean at night.
THEN, our lfs had this HUGE crab, so we got it, and it is so cool. The undy picks on it but it is a quick puppy. "tnt" found the name of it.
Your snails will be okay if your crabs don't want their shell, and the slot in the shell isn't big enough for the fish to get their mouths into them.
That is my recent novice experience with clean-up crews with 3 triggers, Pinktail, Picasso, and Undy. It is all a chance though. Temperaments are different with each fish, just like us humans :joy: ..............Peace