Flat purchased by dad on cousin's name to be transferred

My dad had purchased a flat in Mumbai on my cousin's name in 2009, Out of which my dad paid 90% of the flat money because my cousin's loan was rejected by the bank. My dad, mom , brother and i had been staying in the flat since then. My dad had taken registered power of attorney from my cousin. However the share certificate is on my cousin's name Till date we have the flat on my cousin's name. My dad passed away in January 2019. What can we do now to transfer the ownership of the flat on my mom's or my name ?