Need advice on property partition

Recently my father passed away without making any Will document. For the last thirty years, I stay in a small flat with my mother. The housing society membership is transferred to my mother's name & the electricity meter is also in my mother's name. Now my sisters are threating to evict both of us from the flat & are demanding that the flat be sold so that they can get their inheritance share from the property. I & my mother do not have any other place to stay. My mother has already given my sisters several lakhs of rupees by cheque, two years back. What should we do now?