There's only two ways for that to happen.

1. You listed the person as a reference.
2. Someone else told the investigator the persons name of "someone who knew you well" during the developed reference phase.

Otherwise, they do not go back that far in general. It's irrelevant to your case.

Further, investigators do not make determinations. They have no part in that. They investigate and submit your file. It's you they are investigating, not anyone else. We have people with spouses as convicted felons, parents that has been in prison and others that have been in serious trouble.

Again, as long as the family is not involved with foreign governments or acts to overthrow our own government, the adjudication does not add any weight to those circumstances.

You're free to reach out to verified investigators on /r/securityclearance to confirm.