First of all, you are amazing!! What an awesome thing to do for your family. What about using your slow cooker? I have no experience cooking for that many people, but I do lots of prepping, to spend less time in the kitchen.
I make huge batches of food because I dehydrate leftovers for backpacking trips and using my slow cooker has saved me. You could aim to have something in there every time you're prepping. I buy large pork shoulders and make Nom Nom Paleo's kahlua pig, or Mel Joulwan's chocolate chili. Just google whole30 slow cooker, and you may get some ideas. A lot of people are starting to use pressure cookers more too, and there are tons of pressure cooker recipes out there. Mel Joulwan's website also has a great batch cooking guide. Maybe you could try that, on a larger scale? Just google Mel Joulwan weekly cook up.
I don't know if using frozen vegetables is an option for you? I'm not the hugest fan, but I use them to send in my husband's lunch because he doesn't mind, or if I really just don't feel like prepping. Even if you used them for the occasional meal it would help save time.
As for fat, drizzle coconut oil or olive on the food before serving, make mayo, dollops of coconut cream, there are tons of sauces you can make, but I imagine you want to get away from making more things!