I work 4 8 hour shifts a week, but this is my schedule... My dh works pms, so I come home, take ds to summer school & hop into bed right after I get back, usually between 0800-8030, sleep until 1200, when dh drops off ds from school, I stay up until 1800, then I drop ds off at the neighbors & lay back down until 2000, I get up exercise & get ready for work, my shift starts at 2245. I usually don't eat before I lay down in the morning, I eat breakfast around noon, supper with my ds around 1700 & then I pack a lunch to eat at work. I just started exercising about a month & half ago, I was suffering increased stress & I sure can stand to loss some weight, plus I was exhausted all the time. I've only been a night shifter going on 6months... I'm a newbie myself... I found the exercising has increased my stamina, I feel little stress, I'm not always tired & I have managed to drop 11 pounds. I also don't drink anything but water all night at work... which allows me to drop right off when I get home.
I do have a coworker who works 5 8s, she cannot do what I do & so her 2 children go to daycare during the summer & afterschool programs during the school year, so that may be an option for you. Just realize that most 3rd shifters no matter how they try, never get as much sleep as someone on days or pms. And it is rarely concurrent.
One thing here, I'm one of those people who have no difficulty sleeping anytime, anywhere & can drop off into sleep quickly.... probably helps I only average 6 hours or less a day of sleep, but I was that way before 3rd shift. I do, however, tend to waste my first day off, I'm too lazy & nonproductive. It's definitely doable...but again I don't work 12s & everyone is different. Good luck I'm sure you'll find a way to make it work for you.