I have a family. I could do meal prep for only me and eat separately, but I value eating the same meal with everyone. And I'm not doing meal prep for our entire family.
I do this sometimes for lunches, which we eat separately anyway. But that's only 1/3 of my meals.
This indeed makes it harder. If I wok some dish for 4 people and use 1 tbsp of olive oil, did I consume 1/4th tbsp? What if 2 of those 4 were kids, so I ate slightly more than 1/4th?
Over time it will even out. Also if you weight out the whole dish it's easier.
I'm assuming we're talking about e.g. rice dishes or stews, curries, etc. "one pot" dishes. Otherwise if it's like steak and vegetables, you can weigh each steak and the vegetables, do them in different racks of a steamer etc.
Sure, there are other ways. For instance using different dishes than the rest of your family to limit portion size. You can share most of a meal, but have a specific side for yourself, etc.
I do this sometimes for lunches, which we eat separately anyway. But that's only 1/3 of my meals.