Query Regarding When To Present The Will In FDP Case & Is Probate Must For Will

My mothers elder sister has made a will in my mother's name. Now my mother's sister has expired. Our case is still pending for Final decree. In the original plaint, it is decreed as 1/3 equal share between my mom, mom sister(both plaintiffs) and mom brother(defendant). Now our advocate is not presenting the will in FDP case and he is telling that the witness should present the will before the court. If we are not presenting the will, my mom's sister name will be deleted from the suit. Proper guidance is not provided by our advocate.lf I ask we can make probate of a will, he is telling it not required at all. The Will which is made is registered and it is an open will. When and how to present the will in our FDP case which is still pending. Is probate necessary? Kindly guide me and help me out in a proper channel of how to proceed further in this case.