@Tim-and-Brenda0 I don't know of any way someone can book blocked dates.
Only way I can see to do it is to coordinate closely with the guests. As they have been previous guests, you have their number and they have yours. Ask them to call you, or vice versa, when they are ready / available to book.
Then, take off Instant Book so no one else can IB the dates. Open the dates so the preferred guest can book immediately while you are on the phone with them. Of course, if they are late off the mark you do run the risk of having another guest reserve and you having to decline them - if that happens remember to choose to keep the calendar dates available for your preferred guest or they will be blocked.
OR maybe Airbnb has a solution. Contact Airbnb.
USA 1-415-800-5959 - Toll free 1-855-424-7262