You sound very ill-prepared to own toads. However, it's already done, so we'll try and fix things, yeah?

A dark color in the toads generally indicates stress or low temperature. Do you handle the toads? And do you have any source of heat for them?
They can survive with a small bowl of water, but it is not good for them as their toxins can build up. And even if you change the water every day, it can still cause issues if you don't de-chlorinate it. Amphibians literally breathe through their skin. It may not have immediate effects, but it will cut their lifespan short.
So yes, it would be best if you could do a large portion of the tank with water so that water changes are less often. Even better, you can set aside the money to put together a small filter. You can buy one, or you can make one. Personally, I like to construct my own. Costs less than a filter of similar quality and lasts a lot longer. I can give you instructions on how to make a filter yourself for about thirty dollars that will keep the water clean for a very very long time.

As for feeding, you should feed them about every other day. They won't eat fish, and if they're so starving that they do, it would not be good for them. If you went on vacation, it would depend on how long. A couple days would be fine so long as you give them a big meal beforehand. A week, and you could shut off heat so that their metabolism slows. Any longer and you should just get someone to feed them while you're gone.

Also, how many do you have?