Query on long term capital gain

Dear Friend,

1. You can take a reasonable estimate of the fair value of the land prevailing in that locality during 1981. Alternatively, you may approach the land registrars office to get details on suitable land deals occured during 1981 in your locality and use that value. The second method will be cumbersome.

2. Yes the capital gain will be divided on proportionate basis as there are 2 equal owners.

3. I did not understand this question completely. Could you please clarify whether you are planning to build a 3 storied apartment in the new land purchased?

4. Yes, you may invest in a residential apartment and bonds and claim combined exemption. Buying land alone will not make you eligible for exemption. You will have to construct residential apartment too. 

According to my view from the case of Sushila M jaheveri , Rajesh Keshav Pillai & Rajnit vitthaldas

The Intention of law is that on the sale of one Property (long term capital asset)investment can be made in only one property (residential) and not in more than one property & cannot claim benefit under other section.
Thus from the sale of two properties investment can be made in only one Asset i.e either property or Bonds and not in both of the above

Yes the entire 3 storied building build on the land will be considered as a single building and hence exemption can be claimed.