Property rights of a christian widow with no children

My sister's husband died last year without a will.they are Christians (r.c) and having no children's.they married 36 years back.26 years back properties are donated to my brother inlaw by his father.my sister and her husband ( brother in law ) made a separate house in the above property and are living together .their parents died 14 years back.brother inlaw has 2 brothers and 2 sisters.now they are demanding for half the property.what to do sir. My sister is now 57 years old