It sounds like your players (or at least some of them) want to play a different game than you do. There is nothing inherently wrong or "incorrect" about playing a game in as chaotic a way as possible. However, it's important that everyone is playing the game that they want to be playing. I have a few major points that I want to draw attention to including a set of tips
Don't try to control player behavior
This is one of the easiest mistakes for a new DM to make. It is easy to feel like you are setting up a story for your players to explore, or building a game for them to solve. But in most games, you're not. It's not a video game where a developer tells a story and a player experiences it. Instead, most tabletop gaming is about everyone getting an equal say in the story. If you try to shape the choices of your players too tightly, the best case is that they feel "railroaded" (forced into one plot line / series of events). The worst case is that they resist and everyone gets increasingly frustrated until the game falls apart.
So my number one piece of advice is to throw out the window any idea of "then the players will/should do _____." Your job is to set the stage. You plant NPCs and objects for them to interact with and make those things interesting. Then you turn your players loose on your scene. But in any good game, the players are never supposed to do one thing in particular. The choice is up to them completely.
I promise, if you can figure out how to let go of the idea of control, you will have a much better time.
Talk to your players
At the same time, you should absolutely talk to your players and find out what game they want to be playing. What do they want out of this experience? Are they defining fun by having an open world to cause chaos in? Do they want a meaningful story? Do they want their characters to grow? Do they want to meet cool NPCs? What are their top definitions of a fun game?
Gather information on what your players want and then do some thinking about what you want. See if it can match. If it can't, be honest about that (see below). If you think it could still work out, then bring them back together and talk about what you heard and your own opinions openly.
Set concrete guidelines
Since you have so many different people who seemingly want different things, I strongly advise talking through concrete guidelines together. Maybe this is to stop any one player from being too hasty and getting in the way of others play "We will not harm seemingly-friendly NPC before discussing it as a group and agreeing." Or maybe it's to keep the story moving forward "Everyone only gets one action before the GM is allowed to introduce new information."
These guidelines should be as clear as possible. It should never be up in the air whether they have been violated or not. Everyone should come up with the guidelines together, and you should not include a guideline about "doing what the GM wants" (see point 1).
Having guidelines will help control the chaos and will give you something to fall back on if it gets too much out of hand.
Try a different game
It is possible that your interpretation of naheulbeuk just isn't the same as your players. If that's the case, maybe your group should try playing a different game that has clearer guidelines on purpose or acceptable behavior. There are loads to choose from, and a variety of forums where people are happy to explain which ones might be right for you!
Try playing instead
If you're not having fun as a GM, try playing for a while. I think your player's suggestion to swap places is a good one, since you may both gain some perspective on the other's views. However, some people just prefer to play and that's okay. You might also find that you don't enjoy GMing for this group, or this specific game, but might like it in other cases, and that's okay too.
Roll with it
Let's say you decide to stay on as the GM with this game and are trying to "loosen up." What can you do when your players make such seemingly random decisions? The goal is to just go with it. Maybe it goes something like this:
- Players discover a noble who is eager to talk to them about a problem
- Players kill the noble instead of listening
- Players search the room and find various expensive things, which they pocket
- The guards come in and, seeing the noble dead, pledge allegiance to the players.
- Your players have now conquered a small kingdom. Congrats to them.
- But they've also inherited the curse that is doing ____ and must be broken by going on a quest.
- Players trick someone else into going on the quest for them. (another chaos moment!)
- In the meantime, instead of running a successful kingdom, they go around stealing and pillaging from their people.
- The people riot, how will the PCs handle it?
Maybe they kill all the villagers and the person who went on the quest comes back successfully and so your PCs have a kingdom with no people but at least no curse.
Or maybe they solve the riot some other way and that sparks something new.
But either way, they still had to come up with solutions to challenges. They weren't breaking the game so much as playing the villains. As long as everyone is okay with that, it's fine!
How to deal with uncomfortable behavior
I do want to mention that there is a difference between chaotic behavior and inappropriate behavior that is going to make someone sitting at the table uncomfortable. At the end of the day, you are all doing this because you want to have fun together. If someone is making others uncomfortable, then that goal isn't being met and they have crossed the line.
Your group gets to decide what is okay and what is not, but you shouldn't let anyone cross that line. Casual discussions about murder and especially rape often get to be too much very quickly for some people. You should never feel like you have to allow players to engage in things that are making anyone (including yourself) upset.
I wish you the best of luck untangling this difficult situation. I think that it's going to take a lot of honesty and work, but that hopefully it will be worth it and you can go back to having a really great time with your friends.