I'm glad it got fixed and you got to have the trip you wanted despite misfortune.
You just have to look at it from another angle. Not: "my Christmas almost got ruined, I had to pay to have my car fixed, we had to leave early", but "I had some problems, but my family got together and helped us out, the garage didn't charge me an arm and a leg despite it being so close to Christmas, we got the rental back on time despite bad weather, and we''re all still in one piece. It's a Christmas Miracle!".
...Yeah, I know, I'm much better at finding silver linings for other people than for me. Also, that's a totally unhelpful silver lining. But hey, the aunt & uncle in law got to score some karma points!