@Alysia6 With no communication from the guest with new guest information, I would have declined the alteration request. Alternatively, message the guest for the info and let them know there will be an extra charge, explaining why. Send them a new alteration with the charge and added occupants and let the guest know they will need to accept the alteration before they will be granted access to the accommodation.
Going forward, perhaps add to your house rules that all guests must be registered at time of booking, and late additions will not be accepted.