Partition suit

Mutation or no mutation either give or take away the ownership.  Unless there is a valid transfer transaction, the litigation is open.  Now as the matter is already in Court, please wait for the Judgment.  You ought to have mentioned some more details of the date of your mother's and sister's death, profit sharing in that asset, the stand you have taken, the exact date and claim of your sister's children etc.  

If the property was transferred in your name by way of any application signed by your mother then that can be treated as distribution of property ;

However the property being ancestral and as such your mother could only transfer or divulge her  due share only instead of whole of share. The property being ancestral would be otherwise divided among all of the heirs. Though you can claim extra share of your mother if proved that the transfer was valid.

The property was self acquired by mother (It is not ancestral for her) , and in absence of a will or bonafide transfer from her, entire legal heirs of the deceased on date of her death have such rights for intestate succession.