There is only enough floor space in an 18 x 18 for the tincs (some keepers would say that's not even enough space...). There isn't room for a water area and frogs. Also, your water processing plan would also make the substrate way, way too wet for frogs. Also again, that substrate won't support microfauna, nor will it keep a leaf litter layer for the frogs to live in/graze in.
The sensible path is to set up a fish tank for the fish, and a frog viv for the frogs. Both will be much