I’m sure your guests will be more understanding than you think. It’s a lousy situation but you personally handled it as gracefully as you could.
I can relate to what happened to you: My long-term tenant embarrassed me so much regarding his behavior that bled into the experience of my Air guests over on the other side of my rental ( he played loud music, was drunk, raucous, etc). Like you, I did the best I could to personally go and handle the situation, but I was still livid. The next day I bought some cookies at the nearby bakery and hand-wrote a note apologizing to the guests for what happened. I fully expected a bad review and would have understood their perspective in whatever they chose to relay–turns out, they left a stellar review and were SO nice.
I obviously can’t guarantee this is what will happen to you, but I highlight my experience to say that you might be surprised at the compassion of guests when they see that you’ve done the best you could in trying to curtail behavior that isn’t 100% in your control.
So… don’t dwell on it too much since you’ve clearly done the best you could to remedy the situation. And yep, lesson learned about your dear sister.