Snails work great if your fish don't insist on eating them.
I think this is a thinly veiled reference to a pleco. They only suck other fish if they are deprived of protein. Make sure they are getting their share of pellets and there should be no problems.
You can also attach a sponge to a stick, like a mini squeegee, I have done that, it works well and lets you clean the glass without getting wet (or if you're short).
Mollies are great algae eaters, but may either get eaten by the pollies and cichlids or reproduce until they overrun the tank (like snails.)