Capital Gain on Sale of Unlisted shares and Purchase of new property

Dear Sir/Madam,

My parents had invested in unlisted private cos of my cousin brother.Now  they are selling the shares to my cousin brother at the Book Value of the shares.For Sales Consideration we will consider the FMV of the shares 



1)But for Cost of Acquisition(COA), can we consider the Book Value of the Shares as COA.As taxes are already paid on the Company's profit and PAT is added to the Capital as part of reserves ,can I consider the book value of shares as the COA .In a Partnership Firm,Profit is added to Capital and withdrawal of capital is not considered as Capital Gain.Can we consider it in a similar way?

2)If Book Value of the Shares cannot be considered as COA and actual investment value would be considered as COA,can they pay LTCG without indexation at 10%





3)From the sales proceed from sell of these shares they are planning to buy an under construction home whose possession is after 4 yrs and want to gift it to my sister immediately(in 1 month) after paying Stamp Duty and  GST for the under-construction property

They would transfer the money to her for making slabwise payment to  the builder over 4 yrs

a)Can my parents claim the Capital  Gain Tax  Exemption u/s 54F

b)Pls confirm Stamp Duty for Maharashtra for transfer of residential property from parents to  their daughter would be 200Rs.