Important : We want to get a Probate of WILL done

Hello, My name is Sonam. I am from New delhi. My father purchased a residential property through a property agent in 2003. That Property owener from which we bought this propert died in 2007. He got his legal heirs as 1 son, 2 daughters, and wife. We are having the possession of that house from last 12 years however still we have not got the mutation done.The title of that house is still under that owner. The supporting docuements we have is 1) His Registered WILL which he made in favour of my mother and father, where 2 people signed as witness which is his Son and the property agent (who also died). So now its only 1 witness which is his only son. This WILL came into effect in 2007 when he died. 2) Agreement to sale which is not registered but also includes the cheque no is mentioned in it from which we paid him the money to buy that house 3) Possesion letter not registered 4) Recipt paper not registered Now we have been told to get Probate of WILL done to get the title under my parent name. However the advice for which i need help is if we go to court to get the probate of WILL done, then all his legal heirs might object specially his 2 daughters and wife (there signature are not in any documents) and can claim there share in that house. There is also a possibility that his Son whose signatures are on the WILL can object the legality of WILL and can say that he doesn't know anything about it. Is it possible for us to get Probate of WILL done in this case and what is the chance of our getting this done from court. Please help us in giving right advice as we really want to get the PROBATE OF WILL done. Your help would be really appreciaited.