AITA for not giving back 7K from a vacation reimbursement so my brother can pay Vet bills from his Dog.

Last summer, a family vacation was planned for my family (M40, wife, and 2 kids) my brothers family (M33, wife, 1 kid), and our parents.  The plan was to go to Maui in May 2025. Its easily the most expensive trip any of us have been on.  A fishing trip with dad was booked, a very expensive VRBO was booked and final payment occurred last month, and at that point could not be canceled. These shared costs were put on my credit card and I was fully reimbursed by all parties for their share.  

Last week, my brothers Black Lab had a severe health issue.  The dog was 6 years old and unfortunately it passed.  I got word of it and sent my condolences.  A few days later I got a phone call from my brother.  Essentially he went all out trying to save the dog and has a significant vet bill coming his way.  He informed me that him and his family are backing out of the trip. He asked for his money back that he paid me.  

Needless to say a disagreement occurred between us.  He thinks because he canceled he should be reimbursed. My family and our parents will still be going. The trip can't be changed at this point.   But i'm not reimbursing him, i'm not about to pay another 7K out of my pocket. 

I told him absolutely not.  He's called me an asshole and threatened small claims court.  Its been a pretty toxic last few days.  He refuses to consider going citing finances, emotional distress from the dog, and he doesn't want to be around me.  Am I the Asshole here?