Duaghters share on fathers property

Iam married.My husband,his sister,mother and father..totally they are four in the family.My father-in-law is a school principal.He has his own primary school. Recently my husband's sister (Lekha) along with her husband (Raj) came and did non-sense to my father in law and mother in law.Since from the day they got married they are demanding for money. They have abused my father in law several times.They abused him for not giving money for what they wanted. Indeed they demanded additional dowry.Dowry for every festival and for every occasion. If he is not ready to give money, she will make her husband come home and make him to abuse her father physically and mentally..And now Lekha is demanding share in the property. She is blackmailing her father that that she will file a case in court for her share in the property. My father in law has 90% self acquired property and 10% ancestral property.All this property is on his name. He is not willing to give to her at any cost as they have abused him several times and never took care him off.He wanted to give his property to his son (my husband).So in this case, if she files a case.. will she get the share in the property even if her father is not willing to write on her name.