If you are just talking about unblocking dates you have made unavailable because your family planned to visit (without them having booked through airbnb), yes, certainly you can simply unblock them. I've done this several times, for various reasons. The only circumstances I know of where the host can't unblock dates is if the host cancels a reservation without first contacting airbnb, having them concur that the reason for cancelling is valid, and them actually handling the cancellation. Otherwise a host cancellation results in the "punishment" of those dates remaining blocked. Other than that, a host can block and unblock dates as needed.