In our house, DD (14) is very fussy about food at times, and has SEN so its something she can control when other things are out of control, so we have had to learn to adapt for her.
But she will put together things herself (and has got better at actually cooking in the past year).
I think, if they won't eat meat, you have to accept that. And either do plenty of veg on the side that they will eat and only make enough of a meat dish for you and DH, or so much that you have dinner for you both for 2 nights.
Can you get them to organise salads and prepare things for cooking, even if not start the cooking until you get home - maybe a meal like burgers (meat for you, veggie for them), salad and oven chips/wedges/baked potatoes?
Do you have any freezer space? Could you make a batch of a veggie chilli or veggie curry some night, and freeze a few portions for another dinner or 2 for them? Do the same with a meat curry/chilli another night, but give them the defrosted veggie version, and you put away a few meat portions for you and DH on a future night. So you start a cycle of only cooking 1 pot but reheating a second while rice cooks, and you feed everyone.
Can you do a pasta sauce filled with veggies, but maybe grill or fry the meat separately, and add that to the sauce after you plate up the DC portions?
If DC 12 can use the oven, there may be nights they could put together a dinner of "beige" food - oven chips/baked potatoes/wedges (potato or sweet potato) along with stuffed peppers/stuffed mushroom/veggie patties for them and battered fish/chicken kievs/chicken joints quickly roasted etc for you and DH. Maybe with some frozen veg to be cooked on the stove at the last minute.
Are there any conveniences like the ready-to-microwave rice, or fast cook pasta, or similar, on the shelves at home or in supermarkets you can get to? Even if not normal fare in your house, they may be useful as a temporary measure.
It's so hard when you come in worn out from work in general, and having to face into dealing with food issues, but if the DC won't eat meat normally, I can't see them starting now.