I’m not going to write an entire story, but I will give you some ideas to help start the story. Hope this helps :)
1) The seven sons could end up causing a huge problem, until one of them decides to make everything peaceful. So maybe he could make a potion or something that causes the sons to be so nice and kind, that it just makes things worse. That means that everyone would learn a lesson in the end.
2) perhaps each of the sons had a secret...
3) The king and queen could order a decree that did not allow fighting in the kingdom, so everyone is nice. But everything ends up like the first scenario.