Thank you for the comments. we have been running for 4 years and hadn't had this problem before so it was a new experience. (have had too many turn up! so knew how to handle this and yes booking.com does support you.) They would have been too old for age limits to be in place as they were around 18, however it is good to know that we can say no if the person hasn't told us they are booking for someone else.
We clean their private dining room and bathroom every day but never the bedrooms unless they are staying more than 3 days and then we ask if they want the bedding changed. Towels are automatically changed on the 3rd day or earlier if requested.