In this dor, it is very common for families to have a child with issues with the system. Kids at risk is very common and happens to the “best families.”
Yes, someone should check into the family. And see how they dealt with the child and if they gave their children proper hashkafah. But you can’t hold it against the sibling that it happened. Especially if they are from a large family and have one sibling who either had trouble with learning or frumkeit issues.