Power tends to corrupt, and absolute power corrupts absolutely.
There is no exception to the father and son.
Unlike the traditional royal family members, Crown Prince Sohyeon and Crown Princess Minho are thought to have an advanced view.
They dreamed of a new Joseon Dynasty that was different from before.
First, they were the first people to stay abroad among the Joseon royal families. It was the first and last.
Second, they wasted no time on meaningless grounds. Due to the aftermath of the Manchu War, they went to Qing as the hostage. When they arrived in the capital of Qing, the crown princess got out of the sedan and ride a horse. No one could ride a sedan in the capital city where the emperor lived. Crown Prince Sohyeon also positively wrote in her diary that Qing’s women actively participate in outdoor activities. At the time of Joseon's etiquette, it was impossible for a royal woman to ride horses.
Third, they have expanded the budget of Korean residents with exceptional diplomatic abilities. Qing quit support for them when the financial crisis worsened. There were over tens of thousands of Koreans living there. Most of them were people who were arrested by Qing for their wars. However, they took advantage of the crisis and began trading with Qing. They represent a competent executive. It was natural that the financial problems were resolved with this trade.
Fourth, they worked hard to liberate slaves from Joseon. Back then, slaves from Joseon were very much in Qing. The expanded finances were used to pay their ransoms.
However, Crown Princess Minhoe went continually downhill after Crown Prince Soowon returned to Joseon. The real cause was that Crown Prince Sohyeon stood at the center of the political power threatening the king. King InJo's authority has hit rock bottom because of the war and an ignoble peace. If King Inge hated Ching, he would have removed his right arm from Kim Ja-jeom. Kim Ja-jeom was the center of the politicians who followed Qing.
The feud between King Injo and Crown Prince Sohyeon is similar to King Seonjo and Gwanghaegun. King Seonjo's authority was greatly damaged by the Imjin War. The officials demanded that one of the princes be designated as his successor and encouraged Gwanghaegun as their successor. Of course King Seonjo pointed to Yeongchang as his successor to check Guanghaegun. But Yeongrahhang died at the age of 8.
King Injo was more serious than that. King Seonjo was not captured by the Japanese army and escaped to another region, but King Injo was captured by the army. A huge foreign influence was pressing on King Injo.
In this case, King Injo needed to be wary of Crown Prince Sohyeon, under the influence of Qing.
The person who ceded the throne to another person had an unfortunate ending. It is a very scary situation for King Injo. Crown Prince Sohyeon received a blatant weakness from King Injo. Crown Prince Sohyeon died two months later. His official cause was medical malpractice.
Although the cause of the death of Crown Prince Sohyeon is clearly unknown, it is clear that his doctor had committed medical malpractice. It is unclear whether this was the king's plan.
Crown Princes Minhoe was even suffered after death. After she died, King Inge claimed that she had left a vicious letter to her children. She also said she will avenge her husband’s death when she was alive. Of course, the officials asked for a formal inquiry, but King Inge ignored it. I doubt whether the letter actually existed.
Anyway, Crown Prince Sohyeon is a potential threat to King Injo's authority and the heir apparent to Qing's influence. King Injo did not approve and decides to clean up his son's family after Crown Prince Sohyeon died. The incident was also useful for removing the sons of Crown Prince Sohyeon and Crown Princess Minhoe. In May 1645, the three sons of Crown Prince Sohyeon and Crown Princess Mill were deported to Jeju Island, and the first son and second son died in Jeju Island two years later.