Wondering if anyone has turned an injury in to someone else's home insurance, or your thoughts on this situation?

DS fractured his nose at my sister/BIL's house last weekend on their bouncy house. DS was coming down the slide (standing up and bouncing) and nephew had already gone down but then turned around to go back up. They hit HARD face first.

We have good health insurance so "surgery" was covered minus our deductible/copay. But the Dr. said the damage was pretty bad, he's hoping the bones stay the way he placed it, and there could be breathing issues that we can't fix for 5-10 years because further nose surgery at his age (6) can stunt the nose growth. Post-op is next Tuesday to check how it's healing.

DH is thinking this should go through BIL's home insurance. BIL got upset and said "I wouldn't do this to you" so is taking it personally. I don't want any future issues with son's nose OR any issues with our relationship with sister/BIL.

I'm wondering what the right call is here?