If they haven't taken the payment from your father yet, I would suggest calling the hotel now as, even if they do refund him on check-in, and charge your card instead, he might lose money as international conversion rates on credit cards change all the time. I recently stayed at the W in Barcelona; they charged me for the reservation twice, and, when refunded me, I received about £40 less due to the conversions.....no skin off their back, but I was really penalized!