As always you want to be careful whenever mixing species, The fish themselves wont harm the frogs but they may become dinner for your toads, ive kept fish with my FBTs and have never had any problems. I wouldnt put the snail in there because if he is eaten then the frog may suffer from impaction. Please be careful!
snail shells are digestable calcium would be more worried about some sort of internal parasite or pathogen if if a snail was eaten.
2.0 Bombina orientalis
1.0 Bufo americanus
0.1.1 Ceratophrys cranwelli
0.1 Xenopus laevis
All my arachnids and other inverts listed in my profile