I only just found out about your posting by chance, two weeks later, since you didn't tag me. Please excuse my comment if you didn't think it was appropriate. After all, you are the one who brought up this subject, which nobody forced you to do.
I think what I would have done if I had been in your shoes - I probably would have thrown out the first guest, and honoured the new booking. Or else I would have let both guests stay, by offering my own bed to them, in addition, and staying with a friend, myself.