father property

It is believed that you are Hindu. Your father can give away his self earned/acquired estate e.g. residential plot/land as posted by you, to anyone in his life time as it pleases to him.

You, your mother, your brother(s), sister(s) have share from your father's share in ancestral property.

"your father was emotionally threatened and had registered the land".  If your father is ready to say this thing in the court, then you and your brother can claim share in the property, if you file a civil suit in this regard.

aw provides no relief for stupidity.

"My father convinced us that my sister agreed that she will not claim on the agricultural land, but she did not want to sign any NOC document stating that she will not claim either."

You are free to live in fool's paradise as long as you think.

Why should she sign NOC ?

" I doubt if my father would be ready to say that he was emotionally threatened in the court against my sister and brotherinlaw."

Not at all understood what do you mean.

"My father wishes to continue agriculture in it, and pass the property to myself and my brother. Should we get any NOC document signed by her. Will that be useful. "

You have not replied the following question of Mr Dhingra at https://www.lawyersclubindia.com/experts/father-gave-property-to-son-in-law--608646.asp

About ancestral property, you have not clarified to which generation of your forefathers the property relates. So, your query is faulty in itself.