You ought to give yourself a break. I think you are being to hard on yourself.
Do you really have all that guilt about returning to school because it takes you away from your family?
Despite what any self-help book will tell you, it's tough to schedule time to yourself whether it's to study or meditate. It's true, when the kids are young--toddlers, newborns, school age--it doesn't matter, we're always exhausted--emotionally and physically--and then it's the teenage years and then...what?
What comes next? Does it really continue in their 20s???
I recall rewriting sections of my first book (drafted during the early stages of my pregnancy), late at night after the baby arrived because Drew always did the five a.m. feeding, so I could get at least four or five hours of sleep. So, there I was, in front of the computer, entering editorial changes from midnight until two a.m.
Hardly the ideal way to carry on with a newborn in the house. I finally had to set it aside to work on when I returned to work six months later. I was surprised at how little I was willing to change my lifestyle.
Could it be that's what's going on with you? It takes time to adjust to a new lifestyle.
The kids need time to adjust, too. They'll come around.