They get brittle
Vinegar is acetic acid, or CH3COOH. It reacts with calcium carbonate (which is found in bones and eggshells) to form aqueous Ca(CH3COO)2 plus carbon dioxide. This leaches the calcium from the bones, reducing their mass.
If you get too much calcium you may get calcium deposits on your bones.
There's plenty of calcium in tofu, sesame seeds, collard greens, spinach, bok choy, mustard greens, and black strap molasses. In addition, these foods contain vitamn K and magnesium, which are also important for bone health. Also, animal protein is acidic and leaches calcium from your bones. Plant protein is alkaline and protects the calcium in your bones.
If you have a shortage of dietary calcium: While you are growing your bones will not form properly; After you are adult your body will start using calcium from your bones and you will suffer form osteoporosis.
Too much calcium makes the bones brittle.
When the blood calcium is low, the bones in the body release calcium to supplement it. This is a condition which is known as hypocalcemia.
The calcium is released from bones and absorbed by the kidneys and the intestines, then the blood calcium level increases.
If you don't eat foods with calcium your bones will be weaken and frail bones will lead to fractures or breaks. Others develop osteoporosis because of deteriorating bones.
You can very well treat the bones with acid. What happens when using the acid is what makes the calcium dissolve, and it also helps make the bones more flexible.
Vinegar should decalcify the bones. I.E. The bones are made out of mainly calcium carbonate. The vinegar will break it down. There are other compounds in the bones that will remain so the bones will seem soft.
calcium makes your bones stronger
I don't think bones are made of calcium. Calcium is a nutrition that your bones need to be strong.