Good for you. A good lesson that effected both children. The younger boy will know what to expect if he feels such anger one day. With our grandchildren, it was always - Grandparents' house means Grandparents' rules.
We have two sons who have told us many times that while they didn't always like it as children, they are grateful as adults that we gave them rules and consequences.They appreciate the good sense of values we instilled in them. That they always knew what to expect for both appropriate and inappropriate behaviors and they knew they couldn't use us against one another. At the age of 25, our younger son came to me and told me that he thought his dad and I had done a h... of a good job raising them. He thanked me and later thanked his dad. He told me most of his friends and others his age he was working with were so immature and didn't have good values because they weren't taught to them and nothing had been expected of them when they were younger. Our oldest agreed with him. They are both raising their children as we raised them. I'll tell you that made all of the difficult times raising them almost disappear from my mind because that made it all worth it. There had been times I wanted to give in and do it the easy way. I'm so thankful I didn't. So you should feel good about yourself and how you handled a tough situation and keep up the good work as a grandparent. Just try to ignore the family flack. I still get it from one sil now who raised her sons without too many rules and allowed them whatever they wanted. She and my husband's brother are having problems with them today and they are in their middle to late 40's. Loving children does not mean we let them do whatever they want to do. It means we give them the skills and values so they can survive life on their own once they are out in the world no matter what their age. When a child has no boundaries, the world can be a scary place because while they may not be able to control their anger, there should be loving adults in their lives to help them find the way and keep them safe. Sorry, about the length of this post - I didn't mean to go on so.