A.V.
My grandparents used to babysit us when my grandmother worked nights. She would be up doing stuff around lunch, take her nap, and then go to work. Maybe he could get up for a bit with the kids, take a nap, and then do his work. Or occasionally attend those middle of the day at school things that schools insist on scheduling when many parents are at work. Do the schools allow parents to pick up kids for lunch? Maybe do that on a rotating basis with the kids (even the 14 yr old might like a treat brought to the school if s/he can't leave easily) so that's their special time. Not that it should completely take away from you, but if you give up one lunch a month for the older kids, it might really make their day. And even if he doesn't get a lot of time, he can make it quality time. Does he cook? A special dad-breakfast might be a good way to share time with them.