Welcome and good luck!
I bet you are tired with three boys! My only suggestion is to not worry so much about exercise but just about slowly changing your habits and eating healthier.
I'd probably also look into ways you can cut corners in your life to have more time for rest. IE make one pot recipes, crock pot recipes, make enough leftovers to eat the same meal for your lunch the next day (I love leftovers), etc.
Also don't know how old your other two are but maybe having them help around the house with age appropriate chores would also help you out?
Just take it one day at a time