Ancestoral property sale

The first thing you should check is whether the land is Rural Agricultural Land. If it is then its not a capital asset and hence Capital Gains does not arise on sale of the said land. In such case I would suggest you to take a certificate from Talathi saying that the said village is not having population over 10000. The certificate will help you which facing scrutiny assessment before tax authorities.

If the land is not rural agri land, then LTCG will arise. To compute the capital gain, you need cost of acquisition. As the land is bought four generations back, you must not be having purchase deed or cost of acquisition. In such case, you should get the valuation of land done from Govt.Approved valuer for the date 1st April 1981 as it will be your cost of acquisition and indexation on the same will have to applied over the same for capital gain calculation. The gain arising will be Long Term and hence the same can be utilized in new house property to claim exemption benefit u/s 54F. 

I hope it resolves your query.