Muslim law of inheritance

My father-in-law passed away in 2016 intestate. Legal heirs are one wife, two daughters and one son. Open land properties with clear title deeds were left behind by deceased. Property subdivision done by me on paper as per Sharia law. 1/8th share to wife, balance made into 4 parts. Each daughter gets one part and son gets 2 parts. All agreed initially based on which I spent for surveying, documentation etc. Now son is not coming forward to sign partition settlement deeds. 6 years have passed and he is refusing to interact with anyone of other legal heirs. What to do now as we do not want to go in the way of litigation?