As you will recall, Ben Wong played the Yongzheng Emperor in Gilded Chopsticks.
He is the father of the Qianlong Emperor, played by KK Cheung in Succession War. Qianlong retires as emperor after 60 years, passing the throne to his son, the Jiaqing Emperor.
Shaun Tam plays the Jiaqing Emperor in Succession War. It is the same character as Yu Yang in War and Beauty.
Jiaqing’s first Empress is Jess Sum. She is the mother of his eventual successor, the Daoguang Emperor, played by child actor Nono Yeung. He will grow up to be Sunny Chan in Curse of the Royal Harem.
The first Empress (Jess) has already died at the time of Succession War. Selena Li is Jiaqing's Imperial Noble Consort and will eventually become his second Empress. The character becomes Rebecca Chan in War and Beauty and is made Empress Dowager in Curse of the Royal Harem, played by Gigi Wong.
Looking at Jiaqing’s other concubines, Katherine Ho plays Concubine Yu, who will later be promoted to be Consort Yu, a character famously played by Sheren Tang in War and Beauty. Siu Hoi Yan plays Consort Hua, who is Gigi Lai in War and Beauty.
Also, notice how the imperial crown and robes has been "passed down" through the generations.
See Gilded Chopsticks Connection for map before this era
See The Confidant and Curse of the Royal Harem Connection for map after this era
Related: Beauty At War Connection (map of the same era)