@Gemma8 I would contact Airbnb and ask them to cancel the booking. I was in a similar situation and I contacted Airbnb to tell them that I misunderstood who was staying and it was too late before I could advise them that the account had to be created under the actual guest's name. Airbnb read through the chat thread and cancelled my booking with no penalty.
Do not accept bookings for other people, doesn't matter their relationship. In doing this, you theoretically have no information about the people staying (phone, verified ID... nada!) and if you try to ask for it over the airbnb system it will be masked out. Furthermore, if they are bad guests (God forbid) you can't review them because technically they didn't book.
Also, I never accept funds off the site. There's no garuantee you'll get them and it introduces an uncomfortable element that the cashless Airbnb system removes.