Sir,
Your father has given the money to buy the plot to his son in law. Plot registry in the name of son in law. They have mutual understanding that your son in law will be having half share in the plot and remaining half plot will be in the name of your father. In that case, the registry should be in the name of your father and his son in law jointly. However, since you have cordial relation with your brother in law and you want to get half share of your father to be given to your brother, ask your brother in law to relinquish half undivided share in the plot in favour of your brother with all rights appurtenant thereto. For registration of relinquishment deed, nominal registration charges will be borne by you.
On getting the relinquishment deed registered in favor of your brother, he will be the joint owner of the plot. Since the entire ground floor of the plot has been constructed by your brother in law, your brother can construct the first floor and on getting constructed the first floor, partition the property by virtue of partition deed. The contents of partition deed should be:-
Your brother in law will be the owner of entire ground floor with 50% share in the land with all rights appurtenant thereto and 50% rights in the terrace of first floor
&
Your brother will be the owner of entire first floor with 50% share in the land with all right appurtenant thereto and 50% rights in the terrace of first floor
and the partition deed can be got executed and registered accordingly.
In partition deed it should be mentioned clearly as to who will keep the original sale deed (and as and when required shall be produced by him).
Your brother will be having a copy of sale deed, relinquishment deed & partition deed (if possible two original partition deed should be made for both on paying proper stamp duty)