I can really sympathize because this is my husband too. I'm not saying he doesn't enjoy himself at all, but this is not how he'd like to spend his days and he seems to have less stamina than my 4yr old.
My advice is to not run him ragged; you need a partner to help with the kids, not another person to tend to. With that in mind, don't try to do too much and take a lot of breaks. Also, ask him what he expects and wants out of this trip because you may need to temper your expectations to his, otherwise you might not have a very fun trip.
Also, if it's financially feasible - how about a babysitter and a nice night out at an Epcot restaurant (or anywhere, really) with just the two of you?