Not the answer to your question, you probably know that as you are an RA, the 2nd person charge would not be made. I have no experience of having a 3rd person, but I find the hotel's attitude objectionable.

This 2nd (and now 3rd) person surcharge is common in IHG hotels in Switzerland and Germany. Curiously, when travelling with Mrs Roger, I don't stay at such hotels because I don't want the hassle of a dispute.

We have a reservation at the CP Geneva, which I made after e-mailing the hotel with the question (confirming no 2nd person surcharge), getting no response, then escalating to Ambassador customer service. They at least confirmed the no second person surcharge with a c.c. to the hotel.

You might think of involving ambassador service. Good luck.