I work full time and have one 6 yr old boy. DH goes to College twice a week. There are times where I am more tired than others but in general I would say that the motivation is what keeps me going on and work at night in my quilting.
When I didn't have a quilting room I barely quilt because setting up everything took me a precious 1/2 hr of the little time I had so didn't work. Now that I have my sewing room, I can work on my projects just 15 minutes adn still feel I have done something for myself. When my DH is at home, I would just tell him- "your turn to take care of Nicholas" I need to take time for me" and to my sewing room I go.
I agree that planning will help you. If you have a project going on- I bet you do- plan what you can do in 30 or 45 minutes and let everybody know that you "need" this time to rest your mind.
good luck. stay connected
Andrea