Legal rights for widows regarding ancentral property

Hello, 

I have an question regarding widow's rights in the ancestral property.....Question is as follows

We are living in delhi, there is an aunty residing in neighbourhood with his mother in law and an unmarried daughter. There family compoisition is as follows:-

1. Father in Law (deceased) having 2 son (married) and a daughter (married)
2. Mother in Law (Property owner)
3. Husband (deceased)
4. 3 daughter (2 married and 1 unmarried)

So, this question arised when the son in law of property owner showing his interest in the property after her death and he wanted to sell that particular property. I just want to know that whether there is any right availaible in the property law for the widow (daughter in law) regarding not to sell the property for the time she is supposed to live??

Please suggest some ways

Thanks & Regards