I'd say a 6-8 gallon would be ok for a betta, 2 ADF's and 4-6 PYGMY corys, if you want 'normal' corys then the tank would need to be 10-15 gal+
As mentioned, the problem with keeping ADF's is that they struggle to compete for food as they hunt food by smell rather than eyesight. You may need to hand feed the ADF's with bloodworms either using ur fingers or you can squirt some bloodworm above the frogs head using a syringe.