In-laws adults only events!

My husband and I have an 8 & 4 year old. All of our family live within minutes of us. They are a part of our kid’s lives. My 30 year old brother-in-law is getting married in a different state and the nearest town is about an hour away. The email about the wedding say’s it’s Adults Only and in a bar! He says he wants us there. The thing is since it’s in a bar my kid’s really wouldn’t be able to go. My oldest is has always tried to be close with them. I’m afraid if I go and leave the kid’s with grandma it will break her heart! She was upset when she couldn’t go for his birthday since it was in a bar! And if I don’t go My in-laws will get mad at me.