Hi K.,
I dont know how I could ever offer helpful advise to you, I'm a single mother of only One 12 year old, I feel for you, you must be so exausted, I know how tired I was when my son was smaller and it was hard to do anythig for my self while he was awake, I think what worked for me though was to use what energy I had when I had it, which was after work and before home, I'd go work out after work before I picked him up from daycare, even if it was for 20 min, then I found I was kind of pumped up to do more around the house later, so maybe that might be helpful to do either it in the mornings or after work before your evening routine starts. Now that the nice weather is here, maybe also you could take the kids out for a walk after work too, go play basket ball or tennis, I have a friend with 4 boys who is so amazing and she takes her kids to the High School Track and they all walk around that a couple times for extra exercise and she's lost over 40 lb. Good luck.