Is it illegal for Party A to sell the house privately during the hotel contract period?

It is illegal to resell hotel rooms. The hotel room is only for you in the form of lease. You only have short-term ownership of a hotel room, but you haven't got the ownership of the house you rented yet. Selling the hotel to others not only harms the interests of the hotel, but also deceives consumers, which constitutes an illegal act and is not desirable.