@Mark367 What your seller should do is "snooze" his listing now. That way, there won't be duplicate listings in search results. Once all the reservations are completed, he can Un-list his listing.
Also, the seller should advise the guests what is going on so that it doesn't come as a surprise to them to be greeted by a new host. It will also give them the opportunity to cancel or request that the seller cancel their reservations. Hate to say it, but sometimes guests feel uncomfortable with this kind of change over.
Be sure you are completely familiar with the House Rules / cancellation policy and any other terms the seller has on his listing since that is what the guests agreed to when they booked.