Dear Mr. Baburaj,
I think yours is a very wonderful family. GOD BLESS YOU. It is nice to see that you are anxious to permit your brother to construct the floor above yours and want to know whether UDS in the land can be given to him.
Let me give you the legal perspective to the whole issue.
1. Since the property was in your mother's name, she was the absolute owner of the same. You say that she transferred the same in your name. Though nobody's permission/consent was required, yet your mother obtained the consent of all of them for transferring the land in your name to enable you to obtain the loan and construct the house thereon. Therefore you became the absolute owner of the land and you constructed the house. Legally, you are not obliged to give any share to anyone.
2. However, you appear to be very sincere, affectionate and are willing and ready to help your brother in his retirement days. You only want to know whether it is possible to give the UDS by an individual to anybody (you are not questioning whether you are bound to give), and how it can be done when the original land papers are lying with the bank in connection with the housing loan taken by you.
3. Since the land papers are lying with the bank and the bank would not allow you to part with UDS of the land to anybody without clearing the bank loan, you can permit your brother to construct the portion above your floor, pending your giving him UDS in the land. You can clearly agree with him separately that as soon as the bank loan is completely repaid, and the documents are released, you will relinquish 1/2 of the UDS in the land beneath in his favour. Get this document registered so that there is no problem in future. [In this way, while you will be granting the wish of your brother, you will also not be affecting the interests of the bank which has advanced the loan to you on the basis of the land and the building constructed by you. The agreement with your brother should stipulate that he should not construct over and above what is permissible as per the local body restrictions with reference to the plot of land in question.
MAY YOU BROTHERS LIVE HAPPILY, WITH MUTUAL RESPECT, REGARD AND AFFECTION, UNPOLLUTED BY THE LEGAL ANGLE AND TANGLE.