Relativing claiming on property after giving consent of no claim

When my dad was alive he got a written consent (notrarized) from his brothers that they dont have any claim on our village property and we dont have any claim on their business in mumbai. Post my dad's death they started claiming their rights on the property we got tehsil declaration that the property belongs to my dad and within one month one of the brother put a stay on it. And the case had gone for years but post my dad's death the case has been kept idle (approx 10years) and now they are trying to sell the property. What rights do we have and how can we get back our belongings. Also the district court has guven the house in my dads name and they are threatening to go to court and have a claim on it. They have a lot of money muscle and we dont in comparison to them. How can we fight. And is it possible to fight from mumbai instead going to deoria. And can we put a claim on their property if they are putting a claim on ours especially when they signed that no party has claim on each other property. But the problem is in their property my dad's name is not mentioned.