The secret for it is multi-layered! Unlike the vanilla, you need:
1) Seduction feat of at least 2. You get it by investing ONE point in Subterfuge (3 xp cost, or upon character creation).
2) Use pink/seduction lines in at least one occasion; Jeanette and the NOT handing over to her the pendant.
3) Give pendant to Therese.
4) Be obedient to Therese.
5) Be fun to Jeanette.

Be careful that you absolutely need that point in seduction and more importantly, the pink dialogue with Jeanette. I had a save before talking to therese for the first time (for my previous question about not being able to save them both), but this time that i managed it, i had already lost the conversation chance for first time meeting with Jeanette (during which i also didn't have that extra point in seduction feat).

You know that you did it right when blue lines appear during conflict.

Also, i didn't have any chance to use pink lines during surfside dinner phonecall (from jeanette), like how many guides describe (in steam)... But i got it right this time!

Beats me, i preferred the vanilla over it... Even if only 3 xp i wasted on a skill i never use, i never use it and i never like it, here i was FORCED to take it up on me, so i could have the desirable ending for that quest... Also, saving Tourette gives 2 extra xp points, but having wasted 3 on the stat, i even lost 1 xp, instead of gaining. Glitch or no glitch, damn, the original really rewarded you for raising persuasion and trying hard to do it... This is exactly what i mean for other games though, that sometimes glitches and original bugs are better for the player, than fixing them later on... Well, at least i got my Roleplaying inner nerd all happy and satisfied now! Onwards to downtown!

I'm not aware of that. Have you actually analyzed the dlg file to prove that what you say is true?

Nope, but i saved before talking to Therese the first time without spending my ex to stats, tried to follow the steam guide for tourette (tailored to your patch!) and: Without seduction, i couldn't convince them. With seduction, i could. That guide though states for ALL jeanette dialogues with you to have your seduction line used, but at the point of my save only once i was able to do so, just after returning from hotel.

I apologize, but my ability with files and programming is below zero, that which you say about dlg or analyze didn't even make any sense to me. Sorry. But at least i managed to do exactly what i wanted and now i am further in game already!

Still, thanks a lot for your previous suggestions, your interest and once again, your wonderful work plus yearly dedication!

How much persuation do you need?

I did not have the game before it came to gog and I finished the gog version with a female brujah. I could not save both and I also missed a few other quests.

Now I have installed the plus patch and I start as a male malkavian (complete batshit? background, I am MAD after all). Lets hope I understand anything my char wants to say.

You need i think 5 persuasion. Original needed 6, if i am not mistaken. But here you have to use 1 point in seduction (unless Nosferatu), sweet-talk Jeanette (even hit on her during return of hotel), be extremely servile and don't ask many questions to Therese and pick the exact same dialogue lines the steam guide for this quest suggests. In original you could say whatever the hell you wanted at both of them and you didn't have to use seduction...

I think we agreed in the meantime that you don't need any Seduction, but it makes it easier to score on Jeanette. Also the original was clearly bugged because why would Troika use two variables to follow your behaviour towards the sisters and then never use them at all?

We didn't agree. I tried multiple times. You need to use at least once, an 1 point seduction, during Jeanette dialogue, upon returning from ocean house, without handing over the pendant and taking care not to offend her. You don't need to use seduction the FIRST time you meet her, in club basement. I tried with save game from the point just before meeting Therese from the first time. The steam guide for Tourette is completely right. Without seduction at that exact point, NO blue lines appear later to convince them, at pistol scene. You don't need Seduction if you are a NOSFERATU. But you still need to hit Jeanette with a "hit up on her approach", even if it is in white, normal dialogue, at that exact same specific point (to which she replies: "aren't we rotten dead under the skin" line). Sheesh.

How about you check out the dlg file and choose all lines that have G.Jeanette_Seduce +1? I count 3 in the first confrontation and 1 in the second without the Seduction line. This is the minimum count to get them to reconcile and you can even get another one if your Humanity is not higher than 5 which will remove one if you don't give the pendant to her...