Good for you
Congratulations for recognizing the problem and trying to do something about it.
There is no easy answer, of course. I suggest you lead by example. Keep fruits in the house. Don't allow junk food. Don't go to fast food restaurants. Offer healthy snacks like non-fat yogurt, carrots/celery spiced up with humus. Encourage fun, family sports. Don't watch tv. Praise success. Weigh weekly. Use rewards.