Husband dies without writing a will.

My friends sister a widow, her husband as two apartments in Coimbatore, and he had not transfer the property to wife or son, but in her certificate, his mother name is there. after his death, the rent is being collected by her mother and not even a single rupee is given to her daugter in law. now how can we claim the rent and will the mother in law as the right to sell that property? can she claim the daughter in law to give her equal share separation in 2 apartments, legally. The mother in law has many properties in her name and she also has 2 more sons. my friends sister as a son aged 18 studying 12th standard. can you explain can the mother in law as a heir holder what rights to enjoy this apartments?