Negligence by doctor and hospital management

Hello sir, My mother had brain hemorrhage in Aug 2016 due to that she got paralyzed and after 6 months (6 feb 2017) we had another surgery for bone in her brain. Doctors said she is perfectly fine. But in 16 feb 2017 she got some mild attack. We admitted her for one day and doctors said this is normal need not to worry. After that she is facing more problems like vomiting and headache not able to eat anything. 6th April 2017 we again take her to doctor then after their investigation they said she is having brain tumor level 4 means last stage we need to operate as soon as possible. On 10th April my father got expired after hearing this news. We had operation for our mother in another hospital but after staying 45 days in hospital she expired. Now I want to file a case against hospital and mean while we are taking our mother to OPDs. If they can find this tumor in first operation that they had in Aug 2016 or in Feb 2017 then my mother and father will be live today. Please tell me what actions I can take. Thanks