Maybe, maybe not. It is often believed obese women have less osteoporosis than normal weight or thin women. Fat cells can make estrogen-type hormones which may slow bone loss, and can make androgen-type hormones which may add more bone mass. Some researchers feel obesity decreases bone density, compared to large non-obese women of similar weight. Leptins (hormones involved in obesity) may also worsen bone density.
Theoretical. This is theoretical. Adipose tissue possesses an enzyme called aromatase that coverts your steroid hormone to Estrogens that is osteoprotective, but obese or overweight individuals can get osteopenic or osteoporotic. Skeletal metabolism is a complex dynamic process. Vitamin d, calcium and stressing your bones is the best way to maintain bone health.