Here is a link discussing the correlation between exercise and bone density.
In principle it does not matter whether the exercise is done by doing multiple squats and dead-lifts with a heavy barbell, loading a lean body to weigh it down .....
or you are forced to move an equivalent weight that is hanging around the body as fat, every time you stand up, sit down, climb the stairs etc..
That is not quite true. The body strengthens the bones in response to the extra stresses put on them, either by intensive training (e.g. weight lifting) or by being forced to do other demanding work, like moving around whilst carrying a huge weight over and above the ideal wight for height, gender, and body type.
No, your bones will only loose its "luster" over time. You are more at risk if you are a woman as well.
No, they don't, although most of your weight is from the skeletal muscle within your body.
No, just the meat part of your body does.
No, your bones dont gain weight with you.