Responses
there was a line about the prince being removed as the heir, and it being his only punishment (might have gotten the specifics wrong lol) but he's been hogging all attention and resources that would have otherwise been divided into the three of them. he has all the political power and advantage in the social scene, which means he'd still get his way sooner or later (ie killing his siblings ahead of time, or some other plan with similar effect). ideally, they'd have to ruin the prince's image first entirely, as well as make it so that his allies cannot help. that or death/exile
I don’t get why they couldn’t reveal the crown prince mistreatment of his sister to the empress and emperor. I get their explanation but now they genuinely think the crown prince took such good care of her that she got better and they only think of him in a more positive light. Wouldn’t it make more sense to bring them to see the truth(him strangling her), be in disbelief, and then have the halias be liek my second son wants to marry her and since the palace didn’t treat her will/ she has trauma we’re taking her with us