I think your ideas are exactly on track!
I going to assume that you might be offered whatever they have for dinner. Hopefully, what they offer is a well-rounded meal, including protein, grains, and a vegetable. Choose the smallest portion of protein, half the grain amount, and double the vegetable amount. Every meal you have away from the house, make sure it's a vegetable-intensive meal. Eliminate any drinks beyond water, black coffee, and tea (calorie-less beverages). If you do buy food or cook at all, veggies, veggies, veggies!
Another thing to consider -- embrace any opportunities to burn calories. Offer to take the kids to the park (and play tag with them
), mop the floors, mow the lawn, and wash the car. All those can be pretty high calorie-burning activities while also contributing to the household.