How do we get a person to stop his suit against our annuity?

My sister was living with a man who died a few years before she did. They had separate checking & money market accounts. She had originally left all to her partner if she died first. Since he had passed she left these accounts to her brother. His son feels that he is due the larger of the annuity. He has a suit against it so it can not be paid out, however her brother has not received anything from the son's lawyer. The company that has the annuity says they can't make payments unless the son drops his suit. We don't know who the lawyer is & the son refuses any form of contact with us so we don' know what he wants from us.