Capital Gain

There is a plot of land of which 40% is occupied by family A with a Bungalow on it where Mr and Mrs. A are residing. The other 60% is a vacant land occupied by family B.  There is a proposal to demolish existing bungalow and construct a multistoried building with residential flats on the said plot of land using FSI of the entire plot of land. It is not possible for Family A and family B to do separate constructions on their respective plots. The residential flats (constructed area) would be distributed amongst the family of A and B in the ratio 40% and 60%   It is advised by the Tax Consultant that the very fact that Mr. & Mrs.A are demolishing the existing structure (bungalow) and are constructing new building jointly with Mr. and Mrs. B in which both the families  will have flats would result in their being treated as a AOP. Since Mr. & Mrs. A are joining with Mr. & Mrs.B, the risk on above being treated as an adventure in nature of trade increases. The Tax Consultant has pointed out the risks of the provisions of section 2(31) and section 45(3) of the Income Tax Act. Mr. & Mrs. A are confused and seek advise as to how best to structure the deal so as to minimize the tax implication?