You could have guppies and 'fancy' goldfish together, as fancies are usually kept at a slightly higher temp (somewhere between 70-72F) and actually don't do as well in colder water like common goldfish and koi. This is pretty much a sub-tropical tank, and there are a few fish that are commonly kept as tropical that fit into this range. However, for two fancies you'd need at the very least a 30 gallon tank and good filtration, and that's not accounting for the guppies, which would put you at a bigger tank. And sometimes goldies will eat the guppies, so you would have to decide whether you would want to risk that as well.
As it is, the tank you have is far too small.