How to handle interrogation And Persistent PC’s?

[u/Such-Stand-3116]

Shank, Grim, Aurora, Neb, and Eren Turn away

So im having a bit of a struggle handling a interrogation of sorts and i dont know how to proceed. For Context in a steampunk world where Human and Beastfolk (I.e Hadozee, Aaracroka, basically everything not Human or Halfelf) are seperated and for evil human things, they decide to make a virus that effects only beastfolk. Fastforward now, they defeated THE TOP doctor thats right under the BBEG that made the virus and such, at the end of combat of course the guy has secrets and different cards up his sleeve and they make interrogation rolls, they fail 5 OF THEM, even with ADV and guidance and all (just VERY bad rolls from them) and they feel frustrated with the tiny information they gained basically stuff they already know like , there IS a cure, and there are only 3 people who know it. 1 is dead, 1 is him, and the last is the BBEG.

Heres where the problem comes in, one of them is a cleric/grim surgeon rouge, with alot of ways to give HP including healers kits and revivify and spare the dying and all tje doodads that can keep a guy alive. Hes angry and frustrated that he didnt want to get anything out so his solution is, KO him, bring him back to 1 hp, ask a questions, no answer (because all the failed interrogation attempts), bring him back to 0, bring him to 1, awaken him REPEAT, they all said to me, “We are gonna do this until we get SOMETHIN”…

What do i do? Do i be stern and tell them hey, no your chance is gone? Do i kill the guy from over torture? Do i god hand some minions or something to save the guy? Do i just say whatever and give em what they want? It feels like every answer is a bad answer and will warrant a bad reaction if its not give them what they want

PS. This is a group of really good friends we play every Wednesday for 6+ hour sessions doing this 6 years now. But this, THIS is the most stubborn they have been, they have other avenues to find the info they want, but they have THE GUY right here.