If both your mother and grandmother are overweight, does that mean that you will be too?
You do not inherit fat, just a tendency to become fat. The women in your family may tend to store excess weight around their thighs while the men expand around their bellies, but whether you accumulate this fat in the first place depends on the way you lead your life. If the number of calories you eat each day match those that you burn then you will not gain weight anywhere on your body, regardless of your parents' shape. What tends to happen, however, is that we inherit eating and lifestyle habits from those we grow up with. Kick those habits, eat well, get active. You will not only look and feel better, but you will be creating new role models for your children.