I feel for you. Growing up, my mother had heart and kidney diseases, and couldn't have any dairy or a bunch of other things. My oldest brother was an athlete and had a complicated bulking diet. My other brother was fighting lymph cancer for a long time, couldn't have salicylates or molds or fat of any kind. My sister is a vegetarian. My father was an old fashioned meat, potatoes, veg guy and since he was dad, he got what he wanted.
I'll eat anything.
Because my mom worked, I did a lot of cooking. Meal planning for that bunch was a huge challenge.
Here's what we did - first, a routine. Monday was beef, tuesday chicken, wednesday pork and so on. We started with my dad since he made most of the money and it was good to please dad. Whatever meat was on for the day, we figured out who else could eat that also and with what modification, if any. Usually dad, mom, me and oldest brother (meat has fat). There was something, I forget what, that mom needed to change - oh, sodium, and some other stuff. Then, the main starch - make most of it regular, but some without fat. There are a lot of starches. Big bro and mom couldn't have starch. For sis it was the main part of her meal. Usually it was two starches. And then several veggies, because everybody had stuff they would/couldn't eat. And special food for whoever needed it.
Leftovers had to be clearly labelled.
Frozen veg on sale was our mainstay. You never really know what other veggies are going to be on sale or seasonal special or what.
Another huge thing to explore is sauces. If you are limited in your meat choices, say, if you know 7 different ways to cook chicken 7 different sauces, then you're fine. Barbeque, sweet and sour, cheese-and-tomato, alfredo, teriyaki, etc. And shapes - strips, patties, chunky, chopped, etc. Starches plus sauces also equals lots of choice.
Budget - planning makes that possible. Buy in bulk. Have a lot of sample menus worked out so that you can be flexible at the market.
For some dietary issues, frozen veggies are more tolerable than fresh. It's been a while since I knew the details of that - look it up.
Good luck, and don't make anybody sick!