The plot is pretty stupid. If you are in line for succession and you don’t want to inherit the title, you can simply cede the title to next person in-line. Disowning yourself and registering yourself has the daughter of your own brother, you got to be kidding me. If this happened in medieval Europe, you and you whole family would be a laughing stock. The author could have at least come up with something more reasonable and accurate before applying the “comedy”.
This is why some Isekais infuriate me lol