Amalgamation of plots in Bangalore B katha for construction

HI, My mother gifted the 60*40 plot to me and my brother .Initially me and my brother divided the plot as 20*60 and 20*60 and gift deed to both of us and each of us have individual kaths on our names. 1) As we fill 20 *60 is too small for construct and planning , can we construct the home in full 60*40 and divide it? 2)Can we do Amalgamation of plots again? 3)For Amalgamation of plots should we again go to sub-registration office and register it as joint . 4)What is the best legal way for joint construction and divide as floors later.