Are Grandparents Liable For Maintenance Money For Grandchildren?

HI Sir/Ma'am, I need some insight. I lost my elder brother to a tragedy 3 years back. He was in the business along with my father, however in books, he was an employee drawing a salary. Post his death, my sister-in-law moved to her mothers house along with her daughter. This was purely her decision and was not influenced by my parents. My parents are very attached to my brothers daughter, so much so that they have been paying ₹25,000 a month to my sister-in-law as maintenance towards school fees and others expenses for their grand daughter. Now my sister-in-law has come to us asking for money in the name of 'Security' of her daughter. My father has already paid a huge amount to cover some financial losses that my elder brother had made while he was alive. It was then that we called the family members and advised that my elder brother has taken his share and much more in the property and assets. After his death, now my sister-in-law is demanding money, however she is putting her daughter in front stating she needs money for the child's security. My parents, now madly in love with her, are even committing money, while I have asked them to be practical as they have two other sons and then their further families. What has to be done, has to be done fairly. What do you advise? 1. Are my parents actually by law entitled for their grand daughters monthly expenses after the death of their son? 2. If there is a will which my father makes which entitles some part of the property to the grand child and not to the daughter-in-law, can she challenge the decision in courts? His property and assets qualify for self acquired property and not ancestral. 3. Can my sister-in-law claim a share in his property and against his legal will? Looking forward to your help