@Mojo @xxsad I can think of multiple things, given the context that they are trying to climb the social ladder (as referred to when they talked about trying to befriend the high-ladies and just their behavior in general/QianQian clearly using the dad for his status.
(1) They aren’t satisfied with their situation/inferiority complex. Yao QianQian is still technically a Concubine and the dad was hurt by the mom leaving, (and potentially missing the mom,) making the mom a potential enemy/threat to their position. Wan’Er also seems to think that ZiRan is “still” (never was) in love with JiuQing. JiuQing is also living it up, and has gotten what she wanted anyway. So although they technically “won,” it doesn’t feel like it.
(2) JiuQing is the one who made it so people knew about Wan’Er being a concubine’s daughter, thus ruining their chances of a good marriage. She’s also outwitted them so many times and (so they make think) is the reason why QianQian had her miscarriage and inability to bear a child possibly ever, since she’ll be too old after the 4 years of waiting. They want revenge/compensation.
(3) Wan’Er wants what JiuQing wants. She likes Master Peng (ZiRan) not because of who he is, but his status as JiuQing’s ex-fiancé. General Lin is also desirable because he is even higher on the social ladder and so she wants to marry him. To see him ignore her (pretending not to know who she is, basically snubbing her) is infuriating. She still wants to attempt to cozy up to General Lin while also having ZiRan as a backup.
And JiuQing is currently above them in status (even with her faux identity) compared to them despite them having “kicked her out.” You could also argue that Wan’Er is only doing this because her mother wants it, and she desperately wants her mother’s approval. There’s a lot to support that, if you reread. By herself, Wan’Er isn’t a bad person.
Anyway, they’re surprisingly deep characters. At the same time, we can’t really take them seriously. But it would be more weird (imo) for them to leave her alone when she has, essentially, everything they want; a promising future, a lovely soon-to-be-husband, wealth, intelligence, talented, etc., while they were humiliated by ZiRan’s mother (Lady Peng) and are generally looked down upon by the rest of society.
Hope you don’t mind my little essay! I just really love this series and working on it, and I’ve reread it so much at this point that I have a lot of thoughts on the characters lol 💖💖💓💕💓