A Jealous Husband's Hard Lot: Gladly Kneeling at the Princess's Feet

The first chapter and the second chapter are incompatible. The heroine changes from a princess of one country to another princess. In the second chapter, the country is written incorrectly, and the emperor is not dead. Then in the next chapter, the prince has become the emperor. The prince himself is the younger brother of the princess, and finally becomes the emperor's brother. What the hell is this?

The characters' names and titles were confusing, and the heroine died at someone else's hands. In the end, I ended up with him, but I didn't understand.