Usually. Usually they do, but in some women the volume can be retained.
Usually. Breasts are comprised of fat and glandular tissue. Some women have a large amount of glandular tissue with little fat and vice versa. Fat is lost with weight loss, which impacts the breast.
No. If they're mostly glandular may not.
Yes. Since breast consist of fatty tissue and breast tissue, loosing weight will reduce the volume of fat throughout your body - including the fat in your breasts. Thus the breasts will get smaller with weight loss.