Lady living in the house for maintenance purpose claiming the property

My mother's eldest sister passed away without an heir. Since i used to stay with them for quite some years... I have my belongings in that apartment. Its a co-operative apartment with ownership in the name of my uncle, my aunt was the nominee after his death. After my aunt passed away in 2012, another younger sister started living in the apartment, citing reason for maintenance of the property. We didn't object considering her age (60) & single status. Slowly she messed with house belongings & now started claiming sole ownership of the property, refuses to recognize or let us in. Pls suggest.