Why not reframe the idea that you are not in control because you have to do the cooking to that you have a lot of power because you do the cooking.
My advice would be similar to what people have said.
1 meal plan for the week. Get health ideas from Eatng well, BBC food websites etc.
2 food prep for a couple of days in advance, so breakfast is easy, for you and dh Greek yogurt, chai seeds ( they need time to be soaked in yogurt to be able to eat them) on the day put some berries and a couple of nuts on. This is a good protein meal that will fill you up and simple.
3 Track your foods and calories. Use mypitness pal and log what you eat.
4 Give yourself a calorie allowance, maybe 1400 and log it as suggested in 3.
5 keep meals simple. This ties in with meal planning. Then you are not thinking about what you are having next.
Eg Greek yogurt for breakfasts
Poached egg on wholemeal toast for lunch
Grilled chicken with med style grilled veg for tea.
Have protein and water every meal.
I would get rid of cereal and other highly processed foods., eg biscuits and snacks. I just dont buy them, even when the kids were little.
6 portion control. I fell down heavy on this as I thought ( wrongly) the more the better with ' healthy foods' so I would pile a salad with avocado ,nuts etc. This links in with point 3.
The biggest thing is changing your mind set.
It's easy to wallow and I've been there, but turn that frown upside down. In other words flip that mind set to what you are going to do rather than what you can't.
Your food choices impact your children's future health and food habits,so here is your chance to be a positive role model.
New habits take some getting used to but stick with it.
You may get some resistance but just remind people that your the cook, they can make something else if they want. Tip. Dont have junk food, ready meals etc in the house.
Good luck. It needs to start with seeing things through a different lens!