The Great Prince in Joy of Life was the child of the Qing Emperor and Lady Ning.

The First Prince's mother was Lady Ning from Dongyi.
The eldest prince of Qingyu was Li Chengru.
The name of the First Prince in Joy of Life is unknown.
The eldest prince of Qingyu was Li Chengru.
The name of the First Prince of Qingyu was unknown. In the movie, the eldest prince's mother was Lady Ning. He was straightforward, clear, and open-minded, and had never participated in the battle for the throne. Although the First Prince played an important role in the play, the author did not explicitly reveal his name. Thus, based on the information provided, we are unable to find out the name of the First Prince of the Qing Dynasty.
The name of the First Prince in Joy of Life is unknown.
The First Prince's name was Li Chengru.
In Joy of Life2, the Great Prince was summoned back by the Qing Emperor and married the Great Princess of Northern Qi, making him Prince Heqing. The First Prince led the army to the west and won. He also brought the daughter of the leader of the Western Hu tribe, Ma Suosuo, back to his residence. However, the Great Prince did not cherish Ma Suosuo. He sent her to Baoyue Brothel in Jiangnan for Fan Xian to take care of. As for the plot of the eldest princess, the search results did not mention the specific plot development.
The Eldest Prince's ending was to continue to guard Dongyi. In Joy of Life, the First Prince was Lady Ning's eldest son, and he was stationed in Dongyi. Even though he had lost the right to compete for the throne, he still remained in Dongyi at the end, alive and holding an army. Compared to the Crown Prince and the Second Prince, one was killed and the other had his status abolished. The First Prince's ending could be said to be pretty good.
The Qing Emperor had learned of the private affair between the Qing Eldest Princess Li Yunrui and the Crown Prince Li Chengqian through the exposure of a small eunuch, Hong Zhu. Under the arrangements of the Overwatch Council Director Chen Pingping and Fan Xian, Hong Zhu used the Qing Emperor's suspicious personality to expose his private affairs to the Qing Emperor. The Qing Emperor therefore banished the Eldest Princess and the Crown Prince was sent to Nanzhao. As for the specific details and development of their relationship, the search results did not provide any relevant information.