Prayers offered up for the mental peace of that brave young man. It was still four against one and anything could have happened.
I agree. He did well and has nothing to feel guilty or distressed about.
All that being said, the sister needs to learn that hiding in a closet isn't a particularly effective self-defense strategy. The two of them together, both armed, would have been much more effective if, say, the thugs had decided to rush the young man.