Query regarding succession certificate and Caveator/defendants.

Respected Sir/Madam, My name is Vilas and I am from Thane. I am writing on someone else's behalf. Brief background ================= My parents ( both father and mother) passed away 40+ years ago intestate. We are only two sisters ( daughters ) and my elder sister, who was married passed away 4+ years ago and I am not married. I am last surviving family member. ( blood relative). For my further education, my father had invested in shares but they are in his name. Since both of them passed away, I have given POA to my brother-in-law to lodged a petition to get a succession certificate and represent me on my behalf. We (He & I) are the only legal heir and he has declared his intentions and given an affidavit that 100% should belong to her and representing her just to avoid spending time with the advocate/court hearings etc. The petition is in the "ORIGINAL SIDE" of the court. Some unknown ( to me/us!) person has filed a caveat via Ms.XYZ i/b ABC and Co. for Caveator/defendants. I wonder what my options are or way forward to this situation. Sincerely I thank you for your time! and looking forward to hearing from you.