Is my brother the only one who can file the lawsuit on behalf of my mothers estate?

The hospital overdosed my mother on the wrong medication and killed her. My brother is the executor. He is angry at my sister about another issue so now he says he won't go through with the lawsuit against the hospital. Even though wmy mom deserves justice he is doing this out of spite because he is angry. Is he the only one who can file this? We have already started the process with an attorney and he said our case is very strong. My brother said that because he is the executor we can't do anything without him. Is that correct and if so, do we have any recourse? thank you.