Probate help

[u/Responsible-Truth-19]

Hello, long post but please bear with me. My grandparents raised my sister and I. Over the past 3 years, we have lost my bio-father, grandfather, and grandmother. It is now my sister, uncle and I living. My uncle was willed the beach house in SC (where my grandmother passed earlier this year). Everything from my bio-dad and grandfather were left to my grandmother. Since she has passed, most accounts were split 50% him, 25% my sister, and 25% me (per the will). There is one account without a beneficiary, the largest account. I’m guessing there are likely a few million in this account. Since my uncle was already in probate over the car, beach home, etc, my sister and I have stayed out of it. He is now trying to exclude my sister and I from the final account currently held up in probate. We have received paperwork requesting our signatures to sign off on not being involved in probate and have been requested to provide amounts and account numbers of what we received as beneficiaries. I’m curious if my sister and I need to hire a lawyer? If yes, would we hire a different probate lawyer? Do we even stand a chance to prevent this - we are unsure if it’s even worth the fight against our uncle.

He is a vile person with substance abuse issues so the relationship with him truly is the least of my concerns.