As Jennifer H. mentioned, making freezer meals is a HUGE help. I travel 2-3 days per week for my job, and having meals pre-made in the freezer is the only thing that keeps DH sane most nights! If you're unsure of where to start with that, look up Dream Dinners, Super Suppers, Dinner My Way. These are all companies that have franchises and there may be one near you.
In terms of after-school activities, during the school year I limit my kids to one thing they really love. One daughter loves ballet, the other one rides horses. They asked if they could take piano, and I told them we'd try it during the summer, but if they didn't love it enough to give up ballet and horses, then we were going to drop it in the fall. It's just a sad fact of life that with both parents working/traveling, there is no reasonable way for us to get them to all of the practices, events, rehearsals, etc if they are involved in more than one activities.
If you are thinking about going back to school, you may want to think about hiring a mother's helper. Maybe a local college girl? If she has her own car, she can pick up the kids from school, help them with their homework, get them to sports, dance, etc, bring them home, and maybe even get them into the bath, thaw out dinner for you, whatever you need to have happen so you can get home from work, get yourself to school, have time for studying. Given your and your husband's schedules, I think you're going to need an extra set of hands (and wheels) to get everyone where they need to go!
Good luck with everything! I can feel for you. I'm on day 3 of a road trip now, and I'm pretty sure I will come home to chaos tomorrow. Sigh.