How responsible are we for another's sin?

[JoeBandy]

Ok this past weekend my nephew and his girlfriend showed up at my house needing a place to stay for a couple days. They had rented a home together but the utilities would not be turned on until Monday. His initial plan was to stay at his grandparents ( my in-laws), however, when the grandmother found out the girlfriend was with him she turned them away. She told him she was not going to hell for letting them stay in her house together with them unmarried. I gladly let them stay with me. Gave them a safe place to stay ( his only other option was sleeping in his car ) and fed them for 2 days. The fact that his grandmother turned him away deeply hurt this young man. Was she right for turning him away? Am I responsible for any sin that may or may not have been committed in my home since I did not turn them away?