how to put objection in disputed landT

We are living and using a property since40 years.we have much evidence that the property is ours and also in our absolute possession for 40 years.unfortunately in sale deed the owner of the property is some one else circumstantially.Now the wife of the deceased owner is trying to sell the property.please help and advise how can we stop and object the process.or can obtain a stay in the matter.what is the procedure to obstruct the registry in registry office etc.thankyou