Half siblings and inheritance?

my great grandmother married and had my grandmother, greatuncle, and a few others and they/ve all died. she then met a hobo and without ever marrying him had three kids, two of whom are still alive. My greatuncle was the last to go (he just died) and my two half-great-aunts wrote a letter to the court claiming they were his only living heirs (falsely) because he died childless and intestate. Now a company has contacted my mother and her siblings saying they are heirs. This man was a millionaire and a lot is at stake. When my mom told the company that my half-great-aunts were only half and lied to the courts he said he'd have to check into it and thought it would make a big difference. Are we going to be able to get them excluded from the fortune?