Senior citizen ignored by her three sons

My wife's grandmother is 86 yrs old and bed ridden. She has four sons and my father in law is the third son taking care of her. However, the financial condition of my father in law is not very good as he is a retired and gets pension of around Rs, 2500 monthly. Granny's medical expenses is around Rs.40000 per month which is contributed by my wife, her sister and father in laws elder son who gives Rs.10000 per month that too when we insisted him that the medical expenses cannot be borne only by my father in law. The other two sons (second and fourth) never contribute financially nor do they come to meet their mother. She has slogged all her life for the betterment of her sons and also financially contributed to purchase flat for both second and fourth son. The elder son smartly convinced his mother to transfer her flat is Walkeshwar in his name. Once the flat was transferred in his name, he started ignoring his mother. Now he never calls or comes to meet his mother unless his mother is hospitalized or her condition is critical. She also had a shop in her name which she transferred to her fourth son since he is jobless. The second son does not contribute financially nor he comes to meet his mother. When i tried to intervene and told them they have to contribute equally the medical expenses of their mother, I was told since we are not working and we don't have money hence cannot contribute. All the financial burden is on the third son . His daughter is getting married this December and he is not in a financial position now to invest all his savings for his mother medical expenditure. I want to know how to handle this situation as we tried everything to make her sons understand the situation.