I can't see Steve as anything but a golden retriever. Tony is harder to pick out. My first instinct would be to turn him into an animal that builds and engineers, because that's what he does at his core, so maybe a beaver? Or some kind of nesting bird.

Daemon's I weirdly find easier to peg. Steve's got to have something that's small, but scrappier than you'd ever expect it to be. Everyone's brought up loyalty as well, so a badger. (Hufflepuff=loyalty and all that jazz, even though Steve's almost certainly a Gryffindor.) Or possibly one of the smaller wolf species.

For Tony I would think something bright, flashy, and intelligent, but ultimately solitary, and certainly something that flies. A raven or one of it's cousins, like a magpie.