Question how do i convince Ehrys to go back to Harbingers?
I tried to follow the Wiki says that i need 10 insigt (my main charecters has that) Religion 8 (one of my party members has that) and either religion 15 or Diplomacy 14.

I got characters who has that in my party.

However it doesn´t help i can fire of the first two options
pointing out that withering and rotting is a better form of worship
and deducing that she simply wants a better body and Vatnir can give off a response too, nothing however will help.
I don´t get another option of persuading her to accept herself.

What am i doing wrong do i need to respec my main character to have diplomacy or religion instead or what am i doing wrong here??

This is a really old question so you've probably either figured this out already or just moved on but I found your post when I was having basically the same issue with this quest and I couldn't find an answer to it anywhere else online so I thought I'd share anyways. Your problem probably has something to do with the fact that the way the dialogue skills check mechanic works is more complicated than that. I only really bothered to look it up after my trouble with this check.

[url=https://pillarsofeternity.gamepedia.com/Pillars_of_Eternity_II:_Deadfire_skills#Party-assist_bonus]https://pillarsofeternity.gamepedia.com/Pillars_of_Eternity_II:_Deadfire_skills#Party-assist_bonus[/url]

Basically, it's not adding any of your party members' skill levels directly to your Watcher's, it's giving you a set bonus determined by the sum of the rest of your party's skill levels on a sliding scale where you need increasingly more total skill points to bump up the bonus to your check to the next tier. So say if the rest of your party has at least 7 Diplomacy between them it'll give you a +4 bonus to your Watcher's skill level on a Diplomacy check but you need 11 total to get +5, 16 total to get +6 and so on with +10 being the max bonus you can get but that requires 46 points total. In the end getting everyone in my party to use Oil of Allures was able to bump the summed total up enough for my Watcher's skill level plus a +6 bonus to get to 14 and the dialogue option appeared right after passing the first check