get a tank around 55 gallons, and seperate the frog as they will need special care than fish and a snial.
in the 55 gallon, you can get another goldfish. Basically care is nothing, water changes everyweek, and feed them goldfish food once a day.
But the water changes are critical as goldfish are messy and high ammonia porducing fish. Snails can live with the goldfish, and dont require much.
Frogs, it depends on the type. ADF, ACF, or jsut larger frogs that dont live in water.
aquatic frogs, ADFs, ACF can live in the goldfish water, just remember to keep it clean. ACF will grow alot larger than ADF, and ACFs will eat small fish.