1. IF the 50% Land was Gifted to you, THEN Transfer of "FULL" Khata, to mother name, is illegal.
2. Land = 100% (to the exception of already Gifted 1st floor)
a) Gifted = 50%
b) Balance Land Remaining : 50%
c) Legal Heir : Mother, Yourself, Sister
d) Remaining 50% Land to be divided EQUALLY between Mother, Yourself, Sister
e) ONLY Remaining 50% Land can be Partitioned
f) Earlier Gifted 50% Land CANNOT be partitioned
3. Better to execute a proper registered "Family Settlement Deed", clearly outlining the Partition terms (or buyout terms), in the light of the fact that 1st Floor is gifted to you and whether the 1st floor falls within which 50% Balance Remaining land. This Deed would nullify the Khata entry and the Gift Deed, for clarity purposes and income tax purposes.
Keep Smiling .... Hemant Agarwal