Sale of 50% share in old property

Q. An undivided property of 2 storied building on a 2 katha land purchased by two near relatives, uncle A & nephew B in 1950 in Kolkata. Both of them expired . Municipality taxes are regularly paid by descendents of A & B on receipt of Municipality bill in the name of 'Estate of A & B'.It is presumed A & B was 50: 50 owner as this was not expressed in purchase deed. Therefore descendents of A & B also 50% owner each. Now descendents of B, 2 sons , no other siblings , desire to sell their 50% share to one descendent son of A at some negotiated price as he desire to purchase it. What are the safeguards to be taken as regards : 1. Transfer of Property Act 2. Capital Gain Tax and 3. Is it necessary to bifurcate the property between descendents of A & B by mutation before trasfer of property. 4. Is there any other simple option available as all are Senior Citizens above 70 years of age.