@Erica352 It's possible that Airbnb will be lenient in light of the fact that the bookings are so far in the future, but your situation doesn't immediately appear to satisfy the "extenuating circumstances" criteria, so be prepared for the possibility that you'll be heavily penalized. If it's a priority for you to build on your reputation in hosting beyond next summer, you might consider making alternative arrangements for your family member during the booked period, rather than cancelling all these bookings. Otherwise, you might as well de-list altogether.
I agree with @ONERüF0 , it's best to open up dates only within a time frame you can fully commit to, barring a genuine emergency. The host is fully in control of the calendar, and the choice of whether to use Instant Book, so it shouldn't really matter that those factors come into play here.