'It won't actually help to confess' sure is a stance that Wen Xu disagrees with. He is going to do his best to demonstrate why confessing would, in fact, be helpful.

Exhibit A: this stupidly large knife.

The knife hovers aggressively over Wei Wuxian's shoulder. Does Wei Wuxian have anything he would like to say about his activities last night?

If he confesses, he will not be able to kill them and save everyone.  This is definitely the most quiet any of them have seen him.

Well, Wen Xu's stupidly large knife has a lot to say about that.

Wei Wuxian gets a few shallow slices across his torso, and then the knife returns to Wei Wuxian's shoulder and presses, until the blunt force against the bones there becomes alarming. 

There is a lot of blood. Wen Xu smiles nastily. Does anyone else have anything they would like to share with the class?

"Wen Xu! You are crossing the line! How can the Wen Clan be so blatant!"

Other than that.

Jiang Cheng struggles against the chains without consciously deciding to.  

"Leave him alone!  We didn't do anything."

"Lies! You two fought Wen Zhuliu at Qinghe, did you not? Did he damage your pride, you wanted revenge? Wei Wuxian, you are constantly insubordinate and disrespectful to my brother. Now his bodyguard turns up dead, and I should believe you have nothing to do with it?"

He draws his knife away, only to slam his fist into the wounded shoulder.

"Ah! Since when is insubordination proof of murder?"  He did not kill Wen Zhuliu due to his lack of respect for Wen Chao, that is utterly ridiculous.

Wen Chao and Wen Xu have failed to consider the practical considerations that might be involved in motivating this assassination, because Wen Chao and Wen Xu are largely unfamiliar with practical considerations.

"You have acted like a rebel from the moment you set foot in Qishan! Who else would be brazen enough to do this?"

He whirls to face Jiang Cheng. "Will you answer for the behavior of your servant? Last night, where was he!"

"He was in our cabin."  Maybe Jiang Cheng's good behavior thus far will lend weight to his words?

That does make him more credible, but the answer is just as frustrating. Smack smack. "Are you sure?"

"Of course he is sure! We have all been locked inside all day and night, Wen Xu, you've gone insane!"

Well at least he's getting hit and not Lan Zhan.  "This is as much of an excuse as everything else about this situation."  Hopefully this will keep Wen Xu's attention on him longer, and off of everyone else. 

"You should teach your servant better manners, Jiang Cheng," Wen Xu sneers, and he slices across Jiang Cheng's leg. Maybe this will make Wei Wuxian more cooperative?

Jiang Cheng hisses in pain.

No.  How dare he.  Wei Wuxian suppresses the urge to spit at him.  Isn't it so nice how Wen Zhuliu is dead and he doesn't ever have to worry about anyone losing their golden core.  Isn't it so nice how even in Jiang Cheng hates him for putting them both in this situation he will keep silent until they take them to kill the Xuanwu and then they'll escape and he'll kill all the Wens and no one will lose their golden core.  He'll make sure Wen Xu suffers just as much as Wen Chao, this time.

Wen Xu spends a good five minutes seeing if torturing Jiang Cheng can motivate either he or Wei Wuxian to fess up. He is trying not to actually damage the Jiang Sect Heir too badly, so this involved lots of very slow and painful cuts, none of them especially deep.

Jiang Cheng does not know anything about what happened last night, and neither does Wei Wuxian.  He is very insistent on this, even as he has to rely on his shackled wrists to keep him upright.

Of the two of them, it's better if he's the one being tortured.  Jiang Cheng avoided the previous imprisonments, and doesn't have previous injuries to worry about.  

Wei Wuxian is silent unless directly asked if he did it, in which case he says no.  He spends the rest of the time thinking about how, exactly, we will kill Wen Xu.  All of the options are slow and painful.

This is infuriating. Jiang Cheng finally gets a break and Wen Xu storms over to Jin Zixuan.

Where he can be informed that this is FUCKING RIDICULOUS. Their families have been cooperating with the Wens under the agreement that their heirs would not be harmed during Indoctrination!!! Both the Jiang Sect and the Jin Sect have been well behaved, he has NO RIGHT to do this to them for absolutely NO REASON!!!

Jin Zixuan can be whacked with a plank of wood. (He is in fact going to go easier on him because of the Wen's amicable relationship with Jin Guangshan. No whacks will be hard enough to break bones or cause any permanent damage.)

Whack whack. And what was he up to last night? Did he see anything suspicous?

NO OF COURSE HE DIDN'T HE WAS BUSY BEING IMPRISONED

This is so stupid. All four of them were clearly incapable of walking outside their houses let alone getting into the palace to murder someone. 

Zixuan stops yelling at Wen Xu after enough whacking, but he remains clearly indignant.

All of these teenagers are fucking brats. The main sects had better be glad that the Wen Sect would conquer them before any of these idiots get put in charge.

He does mostly accept that Jin Zixuan isn't responsible for the murder. He definitely seems the most offended by the idea that it would have been possible.

He glowers at the lot of them. "This isn't going to stop! None of us are getting a break until someone confesses, so stop being so fucking stupid."

Time for Wei Wuxian to forget he's being co-operative again.

"Oh, I'm so sorry for you, having to torture prisoners to get them to confess to something they didn't do, your life must be so hard."