Are my poor mice sick?

It seems that Jack may be the dominate one...I also have two male mice and one is significantly bigger than the other. As long as he doesn't look weak, or mope around in the cage I believe he's fine. Also I don't want to be the bearer of bad news but it's pretty rare that vets will check up mice...they're so small and there's really only so much they can do for such a small delicate rodent..best of luck. Just keep an eye out for significant change in behavior.