Ok that is a fine sized tank for ADF's but much too small for mollies. They need a minimum of 29 gal and your tank is 18 gals. They can reach a size of 5" at maturity and being livebearers they have a huge bio-load at that size. Guppies and/or platties would be a fine choice for an 18 gallon however.
One of my frogs attacks my hand when I feed...sometimes other frogs get in his way as well..I'd hate to see what he could do to a fish..just a word of caution there.
ADF's have very sensitive skin so take care you don't use fake plants with pokey's that could injure them and file any sharp edges on decor with a metal nail file. Also make sure all decor is firmly planted into the substrate (which should also be smooth) because they tend to slam around a bit and can get caught if they knock something over and drown, since of course they surface for air. I use all live plants with my frogs and would highly recommend that, or silk at the very least. They will enjoy the plants and spend alot of time in them that way. They are very blind, so feeding in the same place every day is advisable. I drop their food into their favorite cave and now they just know that's where they go to eat. In a community setting you may have to be more diligent and keep an eye to be sure they get to the food before the fish. I used to keep them with guppies and found the guppies would be fat and overfed before I could get any food to the frogs, so it can be tricky. Also ADF's are prone to bowel impaction which causes bloating and often death. To prevent this feed them only frog and tadpole bites and thawed frozen foods like bloodworms and brine/mysis shrimp. I alternate every day between the bites and the frozen foods. In a community setting of course they will get ahold of some flake, which is fine, but pellet/wafer foods and freeze dried foods would be very bad for them.