First off, congratulations on making the decision to start a new healthier lifestyle. That is what it is a lifestyle, not a quick fix. Losing between 30 and 50 pounds safely and effectively, the goal is one to two pounds a week. That is anywhere from 15 to 25 weeks or four to six months. Then maintenance for at least three years is shown in studies as the length it takes to get your body "happy" at the new weight. I don't tell you this to discourage you, but to encourage you. To educate you so you know that there is going to be work involved. You are a cumulation of the choices you make. What you do today and eat today will help you become the person you want to be tomorrow and it will teach your kids too, so they will not go through the same struggles as you have.
I don't know all of your stats (height, starting weight, food intake, support system) and goals. But, as a personal trainer I do know that you can not exercise off a bad diet, no matter how hard you workout and step one is to write all of your food down that you are eating, what time you are eating and see where you are going wrong. Did you not eat breakfast? Do you eat when no one is around? Do you grab a bag of candy at 4:00? Learn your habits and your triggers and go from there. Eat five to six times a day.
Also, with the diet...eat the rainbow, red, orange, yellow, green, blue, purple. You can eat as many veggies as possible. The fiber in it will keep you full. Always eat a serving of fruit or two servings of veggies at every meal/snack. Increase lean protein and cut refined sugar. Plan your meals the day before, plan your treat at the beginning of the week. You will know when there is a bbq, or party. That is the day you get to have your treat, a brownie, a beer, pizza or dinner out. That will give you something to look forward too and you will not go crazy thinking, I haven't had M&M's in three days, I deserve it. No, you will get it later.
Last but not least, is the exercising. Walking is great start especially if you have injuries or haven't exercised in a while, but if your heart rate isn't increasing that is just "me" time. When walking, pick a starting point, maybe the end of a street and jog to the other side. Then walk to the end of the street or from tree to tree. You will also want to incorporate weights as well. That will help with the inevitable plateau. Another tip, have a goal. Maybe you and the family can train for and run a 5k together on Labor Day. Or there maybe some bike races you all can do together too. Scoure the internet. You will find something that sounds fun and exciting to everyone so you are all on the same page!
If you do "fall off the wagon" do not get discouraged. Just get back up and start again. I really do hope this advice helps. I am rooting for you!