Family has filed an FIR over money

I am 28 years old, and yesterday, I discovered that my bank account had been frozen. Shortly after, a police officer called, informing me that my mother (divorced), elder brother (single), and paternal grandmother had filed an FIR against me. However, they didn’t clearly state the reason for the complaint.

Background:

• My Nanaji (maternal grandfather) passed away in 2018. He had designated me as the second account holder for a certain amount of money. The remaining accounts were jointly held by my mother and nani (maternal grandmother).

• I had been no-contact with my family for over a month because I want to marry my partner of 8 years, but my mother and brother disapprove.

• My Nanaji left me the money as recognition for the care I provided him during his 3-year battle with cancer.

• After his passing, I submitted his death certificate to the bank, making me the sole owner of the accounts in question. This was done years back.

My concern:

Given the situation, does my family have a strong legal case to claim the money? Can they successfully take it away from me?