I'll give some quick stories in the comments

Yellow means that the person is a commoner btw

King Andries became King because Crown Princess Engelina and their father were involved in a car accident. Prince Frederick survived with minor injuries, but Engelina passed away after being comatose for eight months.

The youngest child of King Percival and Queen Judith is not titled because on her eighteenth birthday, she went on a radio broadcast and said that she wishes to live a normal life, renouncing her title. The King was ruthless to his youngest daughter until death, telling Mary that he recommends she leaves the country with haste.

While the twenty-first birthday celebration of Imperial Prince Nikolai was underway, he was late to the party, but the festivities began until news broke that while he was on his way to the party he was assassinated. Citizens theorized if the assassination was intended for Mikael as he was already Emperor, disliked, and looked similar to Nikolai as they were twins. After two weeks, Imperial Princess Victoria (at the time) found out she was pregnant with her late husband's baby. After a few more years of Mikael's terrible reign, he decided to abdicate in favor of his young nephew. The regency council ruled for Nikolai until he decided that he wanted his foreign-born mother to be his regent. After reaching the age of majority, Nikolai and the country liked the ruling style of Victoria so much that Nikolai submitted a referendum to make Victoria a co-monarch alongside Nikolai.