How do you handle rift between your spouse and another family member?

I experienced this recently. My wife unintentionally offended my sister during our family reunion. No bias or any favoritism, I equally divided my time and talked to them personally. I listened to the explanations of both parties and ended up leaving them two alone and together. Thankfully, they were both open minded and matured enough to understand each other. Lesson learned for me: No need to bank on the personal relationships, if it can be solved by communicating with each other, make them do so. If you think such arrangement is impossible, weigh who's on the right side and advise the other about your decision.