Admisibility of unregistered partition /written memorandum

A partition documents was formulated in 1991 among my grandmother and her 5 son. Grandfather was passed away in 1984. Partition deed written on court dummy paper pasted with 10 nos. Revenew stamp. Not written on stamp paper neither registered with required stamp duty at sub register office. Partition deed has not contain any plot no. , khatian no. , land area. It contain only place name of the property. Lets come to points~ My uncle had been allotted a bastu open land at per condition that he shall has to left a 3 feet wide gali rasta on front side so that all the 5 brother can use the toilet behind the said land through this gali. The total area of the gali rasta and toilet is 0.5 decimel. Rest area is 1.5 decimel. The total plot area is 8 decimel. My grandfather share is 25%(2 decimel) according to khatian. Problem:- in 1992 uncle has sold 1.85 decimal to an stranger. And gave right to walk the stranger on the gali rasta. Sale deed registered with witness of my other two uncle. My father do not know about the sale. Later all the 4 brother sold the gali raasta to my father in 2014. In our sale deed area of gali rasta given as 0.5 decimel. Now the stranger is objecting me to construct a drain over gali rasta. He said that he has purchased 1.85decimel area. Rest 0.15 decimel area is for his walking. He said that only 1 feet wide gali rasta of 0.5 decimel area is lying for my father. Please guide me. How do my father move against this dispute. If we file partition suite, is court will admit the unregistered partition deed? Please guide Soumitra mandal Adra dist- purulia