[Will]

Well, SE4 isn't exactly made to represent solar systems very well. There's no real sense of scale; IIRC, if you made a scale model of our solar system with the sun the size of a basketball, Neptune's orbit would be about a mile out. And in the stock files, there are only five planet sizes (Tiny, Small, Medium, Large, Huge)...

I don't recall the specifics of the atmospheres for all the major moons -- major as in they're usually noted, not because they're large; thus Phobos and Demios, and Charon would count, even if they are barely larger than an asteroid -- but it would go something like
tiny rock/none
small or medium rock/methane (orange picture)
small or medium rock/oxygen (Earth-y picture)
small rock/carbon dioxide (red picture)
huge astroid field
huge gas/hydrogen
large gas/hydrogen
large gas/methane? (not sure on Uranus' composition)
medium gas/methane? (not sure on Neptune's either)
tiny ice/none

All the moons would be tiny, and the gas giants should have asteroid fields in addition to moons (rings). That's probably as close as you're going to get.