Property Dispute

I am a Hindu male living in a house with my wife and children which was bought by my fathers money and elder sister had also taken some housing loan for the same. This house was taken in 2009 November. This property was under 50 -50 % ownership of my father and sister. My father had verbally reassured me time and again that I will also get my legal share of the property when the time comes. In December 2016 my father made a gift deed and transferred his 50% share as well to my sister and also registered the gift deed. She has also made an NOC stating that the money my father had spent while buying this house has been completely paid by her to my father from [deleted]. All This was done without my knowledge, I just got to know all this 2 days back as my sister is trying to sell off this property. Also my father has been living with my sister since the last 3 years so I am not sure if this gift deed was made willingly or under some durance. My father was also hospitalized just before 2 months before the gift deed was made. My father is 77 and suffering from different age related ailments and memory loss. My sister is now wanting to sell off this house and not ready to pay me any share and wants me to evict the house. I have been living in the house for 9 years whereas my sister has lived for around 1 year in this house as she moved in a rented property near her workplace. She is now threatening to send me eviction notice. Please let me know if I can challenge the gift deed for possible misrepresentation. Can I also ask for stay order for ongoing sale of this house and eviction.