if you are dosing ammonia or adding food there is no reason to add anything alive. Adding guppies will just put guppies through a pretty brutal process.
Any fish you buy from a petstore has a potentiality for bringing disease into the tank. I'd quarantine anything for a month prior to adding them.
Do you have the ammonia/nitrite/nitrate test kit?
If the tank the frogs are currently in is uncycled, they would probably be better off in the new tank. More water volume means less fluctuations, and more time until you need to do a waterchange.