How to proof relinquishemt deed is not forced while making registration?

In 2021 my mother-in-law had got registered land of 1.21 acres of her ancestors property through relinquishemt deed.my mother in law has gave her all rights on property in favour of her mother in 2021 it got registered on behalf this she had taken 1.21 acres as her share from property apart from this land she released all her rights from the remaining properties. But now her brother was asking back land.my mother didn't agree. Now her brother has filed a false case on her that she used her mother illiteracy, not educated and registered on released deed in favour of her. But a actually that property registration has been made in front of him and his sister including my mother in law there on the time of registration. Now is as made case on her.can this release deed can proof in court we are not make froud in registation ,this case will be successful for us or he has the chance to win in this case. Tell me what are the proof we should produce in court we are not make any fraud. If anyone against has said that we did froud through word of mouth can it be considered as proof or evidence in court. Please give me suggestion. case will be succes for law is not agreed for him to give back. Now he has file a f