Transferring 2BHK Apartment And A Plot From My Mother To Myself

Both my parents are expired, survived by 2 siblings, myself (age 42) and my sister (age 34), both married, there is no will in place and there is a 2 BHK apartment in Goa which my sister has agreed to transfer in my name and sister will sign a gift deed i.e gifting her share of right to myself Questions regarding transfer of flat 1) the flat is in a Co operative housing society ( shares are in my mothers name) 2) The flat was purchased from previous owner, but with AGREEMENT OF ASSIGNMENT 3) My sister works in USA and has come down to Goa (India) for holidays, she will be in India till 30th Jan. How do I solve this problem. what options do I have and the best way to do it