Is unregistered will valid

We are 4 brothers & 2 sisters belonging to Kanataka. In 1990, Our father (late retired ACP) made a will in my name and brother's name due to bad habits of other two brothers. Our father got the signatures of our mother and other two brothers. He didn't take signstures of sisters considering it is not required in those period according to law. No witness signature is there, but he got it transferred in our names by removing his name. For transferring also, he got signature of our brothers and mother. In the survey RR My father died in 1995 and also my mother died in the same year. We are paying property tax which is received in our names. We brothers sold some plots of our property in 2005. now our other brothers are claiming partition in property. There is another property adjacent to our on which our father constructed 3 houses which stands in my father's name. My brothers are staying there and also enjoying the rent. Not a paise of rent has been received by us. Another piece of property which was in our father's name has been mortgaged by our brothers as co-pacenors without our consent. What will happen in the court now?