Because fucking Yin Iron, that's why. 

He manages to parry both this and Wen Ying's jab at the big artery in the armpit, but they have him on the defensive, now; he doesn't have the attention to hold both of them off and keep hold of the dark energy preventing horrible things from happening in the holes Wen Ying put in his middle and put any more ouches on either of them. 

Good. They can attack him as long as it fucking takes. 

Eventually they manage to slip enough jabs past his guard that there's just too much resentful energy holding him together and he sort of dramatically goes up in weird shadowy unflames that leave him physically untouched but very much dead when they die down. 

Wen Ying elects to respond to this by collapsing on Lan Zhan in relief. 

That's - unreasonably painful, but Lan Zhan would rather die than express that and cause Wen Ying to not be collapsed on her anymore.

CLING. "Wen Ying, are you hurt?"

Wen Ying sort of wants to downplay her injuries so Lan Zhan won't worry, but she was raised by Queen Bitch Doctor and so gives an accurate self-assessment. 

"I'm cut up in more places than I want to be and I think there's some internal damage from the Yin Iron but I'm not going to bleed out in the next ten minutes. You?"

"What internal damage?" Panic. Lan Zhan is not Queen Bitch Doctor and does not know what to do about Yin Iron related internal damage but she'll figure something out.

"Definitely some deep bruising, maybe a little tissue damage but not, like, an amount that's going to kill me anytime soon." She Very Reluctantly unleans from Lan Zhan and begins approaching the corpse.

Lan Zhan follows closely, unwilling to stop touching her. "We should find your sister."

"Yeah, definitely. In a sec." 

Wen Ying proceeds to hack Wen Ruohan's head off and pick it up by the hair. 

"Okay, now we can go."

Wen Ying is Perfect and Valid and can cut off as many heads off bodies as she wants, in Lan Zhan's opinion, especially if the body belongs to Wen Ruohan.

Do they run into any opposition?

All the opposition they face turns into fleeing when Wen Ying waves Wen Ruohan's severed head at it. 

As they should. Lan Zhan is glad that they can make their way towards Wen Qing's rooms quickly. She keeps a close eye on her wife, watching for pain or worsening of her condition.

(Walking is not very fun, but it's not as bad as when her leg was freshly broken. Lan Zhan swallows back the traces of bad blood in her mouth.)

Wen Ying knocks on her sister's door. 

"Sorry, da-jie," she calls. "I would have given you warning if I had it, but Wen Chao decided to murder everyone while on that stupid night-hunt and I had to stop him and then I had to act fast. But I kept Lan Zhan with me the whole time so I wasn't ever alone and I came straight here! I haven't even gone to make the rest of the Wen soldiers stop fighting the other disciples yet!"

"A-Ying --"

She opens the door and stares.

"Wen Ying you absolute fool --" Wen Qing pinches her lips tight, barely restraining herself from punching A-Ying's shoulder. "You moron --"

Wen Ning perks up inside the room behind her. "Jiejie! Did, did your coup go okay?"

"Yeah! I mean I'm kinda beat up but I won." She lifts the severed head triumphantly. "--Lan Zhan helped. A lot."

"Hm. Sit down, both of you, where are you hurt? You're bleeding, A-Ying -- A-Ning, get out the bandages already --"

Right yes bandages

"Wen Ruohan did something to me with the Yin Iron and Lan Zhan still hasn't told me what her injuries are."

"Something with the Yin Iron." Of course he did something to her with the Yin Iron, because Wen Ying took him on alone.

She huffs and grabs Wen Ying's wrist, touching two fingers to the pulse point and closing her eyes, reaching out with spiritual energy to assess the damage.

Mostly there's just a lot of internal bruising. None of her injuries were going to kill her unless she was remarkably stupid about bandaging her cuts; she managed to keep Wen Ruohan from hitting any major blood vessels and he didn't have much time to Yin Iron at her before Lan Zhan intervened. 

Slow exhale. "Okay. You'll be fine. It will take ten minutes for me to prepare your medicine -- A-Ning, do the bandages. Lan-guniang, where are you hurt." She's already opening her medicine kit.

"Please make Wen Ying's medicine first."

"Lan Zhan, jie just said I'll be fine!" 

Her hands are already busy, but now she looks up to glare.

"-- Lan-guniang I am the doctor here and I'll decide which medicines I ought to make when. I would never neglect the care of my own sister or any patient, which includes you. Tell me."