It sounds to me like you have been very accommodating! Here's how I would handle it:
1. First, I wouldn't assume you'll be getting a negative review, customers work in mysterious ways
2. Your review of the guest: I would keep it neutrally positive, but work in how accommodating you had been. i.e. "These guests took great care of our home. Even though their plans changed numberous times, requiring us to adjust their stay mid-booking (61 days to 36 days), they keep in good contact with us.
3. If they leave you a negative review, I would again be as polite as possible in my response, i.e. "These were good guests. Unfortunately, their schedule kept shifting. The length of their stay shifted from 61 to 36 days, mid stay, leaving us with one month blocked but unsold. The was particularly challanging as the original rate was based on twice the number of nights! We made every effort to accommodate these guests, however after 3 adjustments, we were not able to further make changes. It was a difficult situation, we did our best to be fair to all involved."
4. I would not offer any further refunds, you have already done enough!
Good luck, tough situation.
