Family member claiming a notarized paper is their adoption

MICHIGAN

This is a wild story but I’m pretty worried. An in law and his girlfriend showed up to a family party with a child and they said “the adoption went through this week.” It was a notarized handwritten piece of paper with the child’s mother saying she’s signing over rights and guardianship to the girlfriend. The dad is not involved therefore did not sign.

This all just seems like a mess. The child is currently living with them. But they seem to think this is a full legal adoption.

What kind of situation are we looking at here?! This seems like this could go south very quickly.