Purchase and sell of Residential plot.

Sir my mom purchase a residential plot in financial year 2013--14. To construct a house for jointly for me and my brother . Planning is done on the basis of to sell a residential plot at same town due to location of old plot is not good. The stamp duty value of land is 71 lakh, our purchase cost is 51 lakh including stamp duty. Our Father is retired persons. We all family members pay the costs of purchase ( Father ,mother ,me and my brother), purchase of this plot is done partly through two dead , Now sell part ----- my mother old property which is purchase in 1989 from Rs 50000 /00 only. Selling process is started from fynincial year 2013--14 and completed in financial year 2014-- 15.in selling price we received Rs 52 lakh while stamp duty price is 78 lakh . Construct of house--- in end of financial year 2014- 15 we started construction of house at new plot. Which is under construction . Till date we have expense 30 lakh amount on construction. Now answer my question---1) what is the tax liability on hole of above purchase sell and construction. 2) will we have to pay tax on difference purchase Vale of stamp duty and our declared purchase cost / paid to seller ,which is completed on fy 2013-14. 3) will we have to pay tax on difference sell value of stamp duty and actual declared/ received sell Price. 4) have any capital gain tax liability while we are constructing houe. 5) my mother having a house on gifted plot of my maternal grandfather can we clame deduction of capital gain in 54 F.