How to remove old Apple ID from phone without password

My father recently passed unexpectedly. He had several old phones in one of his junk drawers. I was going to give them to some family who could use a phone but they are still linked to his old Apple ID and we don’t have a password. I tried the reset with his phone number but is had since been disconnected. How can I fix this. I am his daughter, it’s just my sister and I. We have an affidavit of heirship as well as the death certificate idk if this would help?