Property dispute

My father mortgaged his home for my sister marriage in 1979..that time not a single paise in my parents home in that stage I started to Mumbai for work to save my sick parents and one younger sister.. That time I was17years old. I got a job in a pvt company in Mumbaiport as a ordinary clerk I worked day and night to save my family and the remaining one sister marriage expenses My father also suddenly passed away in 1983 without will.. I paid the amount with interest in 1986 for the mortgage home which was mortgaged by my dad the wonder is the mortgagee is my own yelder sister . I carried out the younger sister marriage in1986.. I have total 3 sisters all are married before 1987...in this show My mother gifted the house to me in 1997 she is also passed away last year.l. Now all 3 sisters threatening me to sell the house for their share..the fact is the mortgagee is my first sister my dad mortgaged the house for second sister marriage third sister marriage was by me.. Please give right advise.