Buying an undivided portion (1/6th) in a two storied house.

Respected Sir, I reside in the first floor of a two storied house in kolkata of which my mother (myself being the only son) entered into a sale agreement with the original owner by paying FULL (except Rs. 10,000/-) consisideration money and got possesion (WE ARE IN POSSESION SINCE 1986) but she went on to ask more money for execution of conveyance when my mother had to prosecute her under "Specific Performances of Contract" The owner died issueless and without will and at present the property has six owners and the suit hasnt yet been decreed. 1 such owner wants to sell of his 1/6th undivided share and give me vaccant possesion of the ground floor. My question is that he is offcourse a Defendant of the said suit. Therefore can he sell 1/6th share of the whole premises and if so - how is he supposed to withdraw his portion of the pending suit which he is ready to do ? My lawyer initially said that both can be declared in the same deed of conveyance where he will compromise in the suit. Then he said - he will sell total undivided share 1/6th - which is illogical as 50% of the property is litigated by me. PLEASE SUGGEST A WAY OUT AS TO HOW TO DRAFT LEGAL PAPERS? I AM READY TO PAY ADEQUATE FEES IF I GET A FOOLPROOF DRAFT OF CONVEYANCE AND WHAT IS TO BE DONE TO GRANT HIS PORTION IN THE SUIT OF 'SPECIFIC PERFORMANCE OF CONTRACT' Myself being the benefiary to both should make it easier. Please advise, MR. PRODIP MITRA