My Grandfather sells his property to one of his daughters denying share to my mother

My Grandfather executed sale deed selling his self-acquired property to his younger daughter(my aunt) recently. This Sale deed was executed intentionally to deny share for his elder daughter( my mother ) in this property. My Grandfather had only 2 children (My mother and Aunt) My mother was expired 5 years ago. We are 2 children ( myself and my sister) to my mother whereas My aunt have 3 children ( daughters ). My Aunt(who purchased this property) has been living with my grandfather in the same property since past 9 years and now continue to do so after this transaction is done. Please note that my Aunt belongs to same town and her husband works overseas. So she found company and protection in her fathers house for those mentioned time and finally ended up convincing him to sell his property to her. We understand it as a conspiracy by my Aunt to get full share of my grandfathers property. This transaction is still kept under wraps and i came to know about it only after inquiring up with concerned revenue authorities. This came as a shock to us as we were maintaining healthy relationship with our grandfather. Transaction was executed in April 2021. Can we take any legal action to claim this sale deed is executed under family conspiracy and we were denied property share intentionally ? Grandfather is 77 years old and Alive.