Well, you really shouldn't keep different species of frogs together. The toads, northern green frog, and bullfrog need to be in different set ups. What they are in now does not look like a good set up at all. You really need to clean that water bowl.

The bullfrog will require a 100 gallon enclosure, half water and half land. The water needs to be 12 inches deep, with a slope made up of rocks to alow easy access to the land. Bullfrogs get really large, hence the need for a 100 gallon set up. I would not recommend keeping him. They do best near ponds or rivers, not in captivity. If you decided to keep him, you will have to invest in a large filter for the water part. There are tank dividers available at local petstores.

The toads will require at least a 20 gallon set up, relatively dry area. They don't need that much green foliage, so you should try to mimic a forest floor, with dry leaves, a 4 inch thick substrate ( coco fiber is a great substrate ). They need lots of hiding spaces, so get a couple of hollow logs cut in half (also available at petsmart).

And the northern green frog (a.k.a. leopard frog) will require a 10 gallon set up, also half land half water. You will need a filter for this tank also, and the water level only needs to be 6 inches deep. The land part of the enclosure for this frog needs to be similar to the toad land set up.

Each of these frogs will require their own enclosure because frogs have different toxicity levels, and since they will be sharing a common water source one species could suffer from the toxic nature of the others skin. You mentioned your parents not wanting them in the house... the frogs need to be in the house.