Witness retraction from a gift deed

Witness is eyewitness for execution of any document.. how can he now retract... and witness is only to verify signing person he has nothing to do with contents of agreement...

Hello sir ,

My mother is one of the legal heir of that property . My grand mother executed a deed in favour of my uncle , even my grand mother doesn't about this as her mental health was good at that time and she died few months back. In that gift deed my uncle took signatures of my mom and aunt as witnesses. Both my mom and aunt doesn't know about the content in the document.

As per muslim law is it possible to retract her sign from that deed ?

If they goes to court and if they call them as witness then they may think what can they do.until be quiet.