If I made contact with a relative or someone made contact with me. Provided that they are interested in their roots and I don't get the impression that they're a weirdo, then I'm more more than happy to meet up with them.
I would however suggest email as a more convenient method of communication but if they really wanted to meet up and I thought that I might get more info out of them face to face, then so be it. Obviously, if I felt put out or really really didn't want to meet them, then I'd politely put it off.
If I was concerned about being alone with them, then I would meet them in a public space.