First, your diet. Watch your carbs. You probably eat too many. Easy, I do too.
Second, soda, coffee, most juices, ... forget they exist. They're not for us, you & me.
Third, 12hr shifts suck, but your working, providing for your blessings. (I like that.) Start with some simple no-weight calisthenics during breaks or after work.
Muscle tone, endurance work (the best you can manage) are important, but your money should be on the diet.
Can you lose belly fat and keep thick and throned thighs and a lot of people tell me that you can get a toner butt by doing squats is this true?
Caffeine... metabolism accelerant. If I burn through all the calories I eat before I exercise, then I've no energy for my workout later.
If I caffeinate daily, I'm burned out by day 5 of my 20 day exercise cycle.
Thought I would throw my 2 cents in the ring...
I'm a single father of 2 at 40 and I find that when my son joins me, it makes it so much easier. He's a real trooper and we motivate one another. Granted we get up at 6am to do the Insanity but he's doing it and we keep each other going. We are in week #4 and still going.
Time is tough.. I know. I find myself working out either late at night or early in the morning.. and I try real hard to keep the kids moving. We go on bike rides and do Just Dance on the Xbox.. Buring more calories than you take in.. that's key.
Good luck man.. and keep doing what you can.