@Neko-min
Lmao it was not hinted Mao Mao is a princess, it was hinted that the emperor's brother(mentioned many times to be sick) is actually the emperor's son, thus the crown prince. In the chapter Mao Mao theorizes about the baby swap it's strongly hinted at another character being the swapped baby.
About Fao Shen and Rakan: they made a plan so Rakan would be able to buy her aka take her virginity and get her pregnant(her price was inflated because there was 2 rich guys bidding on her).
Alas Rakan's family were not happy he was involved with a courtesan, so they sent him to the war and blocked his letters he sent to Fao Shen and vice versa. He thought he would be back in 1 year but actually it took him 3 years to come back. He didn't make the connection of what would happen to Fao Shen now she didn't have what made her a high-sought courtesan, not until it was too late.
By the time he came back Fao Shen was already sick, granny wouldn't let him enter(Rankan started thinking Fao Shen was dead) and Mao Mao was already with her foster father/Rakan's uncle.
Now this part is not clear to me but I guess before he could take Mao Mao in he had to be the head of his family(he did this also as revenge for what happened) but when he went to get Mao Mao, she already didn't like him/hate him I guess.