Enquiry on Family Pension of a retired Cental Govt.Employee?

One of my old aged relative was a central govt. employee who retired in mid 1975. His wife passed away due to a carcinogenic ailment. He is presently aged around 93 years, who have a son aged approx.60 yrs.old, who is a total mentally retarded with ill health and is fully dependant on his father for the last 35 years. The pernsioner is also having two younger son & daughter both married & staying in nearby area. He is staying alone with his mentally retarded son in a very shabby condition.He is having a persisting mental agony for this retarted son and want some arrangement for his crippled son before he passes away. The pensioner confides on her married daughter rather than the married son. So he wants that the family pension benefit to be passed for the maintenance of his retarded son by nominating his daughter.His financial standing otherwise is meagre for his son’s maintenance after his death. Can anyone provide detailed guidelines as to how the pensioner can make such arrangement.