Xiao dynasty

The Xiao dynasty is the reigning family of Liang.

The Emperor's siblings
The Emperor has two named sisters: He has several named brothers, and probably more:
 * Grand Princess Jinyang,
 * Grand Princess Liyang
 * Prince Li
 * Prince Qian
 * Prince Ying
 * Prince Ji

The Emperor's children
Several other princesses are implied, Jingning being the youngest of them, younger than Prince Jing but older than the Ninth Prince.
 * 1) Xiao Jingyu, Prince Qi, First Prince
 * 2) Xiao Jingxuan, Prince Xian, Second Prince
 * 3) Prince Xie, Third Prince
 * 4) Xiao Jinghuan, Prince Yu, Fourth Prince
 * 5) Prince Huai, Fifth Prince
 * 6) Xiao Jingyan, Prince Jing, Seventh Prince
 * 7) Xiao Jingning, Princess
 * 8) the Ninth Prince
 * 1) the Ninth Prince

Show
In the show, their order and names are changed: And several unnamed daughters. Empress Yan also had a son who died in infancy and should be close in age to the Third Prince.
 * 1) Xiao Jingyu, Prince Qi, First Prince
 * 2) Xiao Jingxuan, Prince Xian, Second Prince
 * 3) Xiao Jingting, Prince Ning, Third Prince
 * 4) either Xiao Jingli or Xiao Jinglin
 * 5) Xiao Jinghuan, Prince Yu, Fifth Prince
 * 6) Prince Huai, Sixth Prince
 * 7) Xiao Jingyan, Prince Jing, Seventh Prince
 * 8) either Xiao Jingli or Xiao Jinglin
 * 9) the Ninth Prince