I'm looking for "out of the box" solutions and "how to debate this" techniques for a very "group and players" specific issue
Looking for experience backed advices, ideally.
I did search for similar questions on here, on the tags I use here. I searched on the matter a couple weeks ago looking for advice that I ended up using, which had some success. I thought it had worked, but apparently it did not.
The 'How to debate this' part of my question is due to the fact that I play an online game in English, while English is not my first language. Getting vocabulary on more technical gaming/RPing concepts and theories in English might help me . I know this isn't tackled in any D&D sourcebook.
The "out of the box" solutions part is because I thought I had dealt with the situation adequately over the course of the last 2-3 weeks. I did so mostly in-character and a little bit of it was done privately with the problem player and GM after a session. I thought we had reached an understanding. After that talk, we exposed "the understanding" to the rest of the group. It was well received.
The curren problem
Now we're 2 sessions after "the understanding" and I've noticed (and then inquired and confirmed privately with others) that there actually are more frustrations than before on how the situation evolved. 4We can actually feel the tension, even online :O
#More on the context
We have a very new group: 5 players with a GM. I'm one of 2 original players, but this is still a new game (we're lvl 3, almost 4 in D&D 5E).
Everybody but me, the GM and another new player are new arrivals in the game.
Others (and the problem player) joined midway through our game. We have a moderately experienced player that I brought in from my other online game, 2 new players that our GM started playing with 1 year ago: they're comparatively new players/GM.
The GM is often overwhelmed by the amount of stuff happening during the game, but he impressed me by the way he ends up managing it all in the end (even tho the flow of the game sometimes suffers for it, he's being patient and his rulings have been fun and were clever IMHO).
I am not quitting this game: I want to help a friend
This issue could be simply answered by "quit this game, find another one" but for the GM, I wanna stick with it and succeed at helping the group solve this issue and stick together. To my eyes, the potential is there.
Me and the 'problem player' both have over 30 years experience playing D&D. I played 50-50 DM/player, he says he's been a player for 30 years. I say that, since it kinda mattered at some point in our discussions, I do feel like he started listening to me when I mentionned my experience. I don't feel like that is a matter of pride nor a fact that would or should give us any power over others in or out of game, but here it is, needing to be mentioned since it apparently matters (aka the problem player brings it up, the new GM asks me for advices, yadda yadda).
The GM often admitted to me, privately, that he has issues with the 'problem player'. He says it is because others have issues with him, which influences him. At first, I tried defending the 'problem player', being a good mediator. I also defender other players' arguments, since they are valid too. When I tell the GM how I think he should deal with it (while also telling him it is not MY game nor MY choice to make), he ends up shying away from actually dealing with it. I have been told my suggestions were good with everyone by the GM himself, I also confirmed with other players privately, it seems true.
Yet, we're still having issues with the 'problem player' privately, which annoys me since I kinda put myself in the middle of it and this is really starting to ruin my fun (and others' fun too, besides the GM and the problem player who both seem content in the end).
More details on the very specific situation
The thing is, I think the 'problem player' is being brilliant and fun, but the GM and 2 other players are having a lot of issues with what he choses to do and can very well do, in character. The underlying issue which caused all the problems in the first, which I had thought I ended up dealing with perfectly, is the fact that we had to deal with his warlock 'Pact of the Chain' feature and his Imp familiar.
Long story short, when he first joined, he didnt know how to play his familiar (like me, he sometimes suffers from 'previous-editionitis').
We played the familiar's ability to attack in combat wrong on the first game, the Imp was basically an additional character that could act as any other instead of the lock having to use an actual attack action and the Imp using his reaction action to attack.
After 2 games of such shenanigans where the Imp actually was the strongest character on the board, I decided to intervene after I talked it out with the GM.
I decided to take 15 minutes before the actual start of a session, when everyone was online, to have the difficult Discord discussion we needed to have about how Warlock's Pact of the Chain familiar actually worked. At first, there was a lot of resistance, but when he read the rules and saw explanations from this site, his 30 years of experience as a player showed and he 'said everything right' and I thought the matter was settled.
Now, two games later, we play the Imp right but now we have come to realize that the Warlock is evil. He's been caught stealing loot from the party (which we knew of OOC, but not IC, since the PC is a Yuan-ti, doh!) and things have gone downhill since.
The fact we have another member of the party, a chaotic neutral rogue, who also steals from the party (he's a new player, but smart enough to realise he cannot afford to steal "a lot" at a time) created the whole situation. The rogue actually learned that the stealing was happening (he didn't even know OOC, since he often isnt paying attention).
Now, he started paying attention and things are getting worse. The Imp was our de-facto scout, but since the group doesn't trust it (IC) anymore, this role went back to the rogue, who has doubled down on him stealing from the group "to compensate for what I didn't get a chance to steal" being his OOC explanation of his IC actions.
I'm at a loss on how to proceed next, even tho I have ideas
We're playing an official module, leading to another official module.
I thought bringing up the technicalities about how characters are supposed to "scale up" in power, the amount of "value" they should have access to as far as magical items go, might be a way to put everyone on the same page, but I've been met with classic "IC excuse" for an "OOC issue in the group dynamics" like: "Well, my Yuan-ti is a power hungry exile that wants to amass enough power to go back to his people and exact his vengeance" to "my rogue character would not actually care about all that".
At this point, I'm thinking "in character solutions" are as viable as OOC ones. My previous character died 4 games ago and he was the soul of the group, able to maintain some kind of order in all this chaos. He also was the tank and strongest character of the group - which my new character also is even though he is not as efficient at it (both from his background and his features).
I'm used to dealing with this kind of issue as a GM and my technique is usually to "nip them at the bud" before it becomes a problem, finding a viable solution for everyone or being firm about the rules as written (or the Rules as interpretated by the GM, me) or coming up with other more unusual solutions to everyone's liking.
Additional conundrum: should I even bother with it ? Should I take that responsibility or will this cause more issues because I'm actually a player and not the DM ?
Can mediating work in the context of D&D group dynamics ?