i'm just curious and this is an honest question - how do you know your dog was diagnosed with a problem if you haven't taken him/her to the vet?
You NEED to sit your family down and explain that if your dog does indeed have a health problem that stuff NEEDS to change. Diet and portions HAVE to change, and exercise NEEDS to be done daily. Reduce the amount of food given, this is a MUST first off. Try substituting part of the meal with green beans. For example; if you normally feed 2 cups of food a day, try instead feeding 1 1/2 cup of kibble and 1/2 cup of green beans.
Also make sure you are feeding the SAME sized portions every day. Getting a quiktrip cup and filling the bowl to the brim are not measured portions and can also be cause for overweightness. Get a measuring cup, read the guidelines on the back of the bag and feed accordingly. Measure out the exact same portion of food EVERY TIME.