My elder's sister husband expired due to neglegence of hospital.

Dear sir My Elder's sister husband named Dilip pal, resident of Kalighat, Kolkata died on 14 February 2016 in the hospital of Sambhunath Pandit at elgin road in Kolkata. He was admitted on 13th February at about 4 p.m. patient was suffering with diabetes and the haemoglobin found 6 mg before 20 days of admission in this hospital. He felt breathing problem suddenly on 13th February and my sister and 17 years old son rushed to the hospital carried him. The doctor of emergency admitted him but did not care to patient while the patient was restless till 14th February before death. my sister and her son requested to the attended nurse to call the doctor but nurse ignored the matter saying doctor will visit on Monday i.e. 15th February and see your patient instead of initiative step. I think blood transfusion was essential while the patient has less haemoglobin and required ventilation at that moment and at 3.40 pm on Sunday dated 14th February, the patient expired . The hospital issued Death certificate mentioning chronic kidney disease and diabetes mellitus while the kidney was not effected in the report of test . In the above circumstance , I request you that your co-operation will help me so that I could get justice against this kind of negligence doctor.