I completely understand your pain. As this is growing more common and since we cannot change people, the only workable solution is to have proper old age homes or community homes. It somehow also speaks of the poor values inculcated by your brother and sister-in-law. In such instances some other child should have stepped forward and taken care. Anyways what is done is done. One must learn the lessons and move forward.
Affectionately,
Alok Da


