This is crazy! I'm glad you managed to cancel. How rude and entitled can some be to do something like that. I'd personally be furious!!! Actually I was because something of similar nature has happened to me.
I had a couple in their 60s book my house and the lady told me she's been a vrbo host for 15 years. next thing she's asking me if her sister could see the house. Me (stupidly) said yes, sure, the house is empty tomorrow let her come by.
Needless to say she inspected the house trying to find faults, like a buyer. Opened every door, every closet, inspected everything, the oven, the fridge, the closet linen which was closed and wanted to see whats inside and why do i keep it closed.
She got on my nerves so bad that I called the person who booked and I yelled at her to cancel because her sister was disrespectful and I am not comfortable with them. They tried to blame the sister but did cancel.
Now your story is even worse. I hate these people who feel entitled. Your guests were horrible!