Undivided share of dwelling house - co-sharer made a gift deed without my knowledge

My grandmother house and shed part gifted to A(Aunt),B(me) and C(big father's son) in 2004. I am B. House consist of Part A + B and shed consist of Part C(now he built house). C was residing in ground floor of part A+B. I removed him after long battle of civil suit for eviction. Finally C made compromise and when to his side part C. We made a MOU in court that he got money n vacating the house in Feb 2018 and no further claim and the whole house is in my possession. Now part A my Aunt gifted to C without my knowledge in Feb 2019 Please note: my Aunty never in possession r she never accepted her gift. It was always in my possession n she's living in aboard. My question is 1) How to make cancel r invaild that gift deed registrated without my knowledge? 2) how can I safe guard myself because I don't want to sell that house. It was my grandmother's house. But my Aunty wanted to sell that house and get her share. So she s doing indirectly by gifting to him. She's making litigation again in my peaceful possession. 3) she didn't have possession of her gift part A How can she do gift deed by says she pays taxes n all dues which is absolutely false. 4) whether she has rights over her side or not because she didn't accept her part A till now between my grandmother died in 2013. 5) what are the problems I am going to face from them. Kindly please give your opinion on this. Thank you in advance.