A few questions about African Dwarf Frogs?

The frogs will most likely be fine in the water conditioner you use but I'm unsure about the medication. I had an African Dwarf Frog with my Betta and the frog used to attack the fish and bite its tale, so I wouldn't keep them together, but with a 4 gallon tank that's pretty huge for this type of frog they may not even see each other. I don't know about the feeding but if you just give them frog/tadpole bites a couple times a week you should be alright. Yes you can keep the same together. There is really no need to test the water quality just change it and clean the tank at least once ever few weeks and you'll be fine. The frog will not grow beyond 2 inches as long as it's an African Dwarf Frog, the website you provided is for African Clawed Frogs and they can grow to over 5 inches.