I have to bring this up. As i wish to be able to edit your companions like you could with your own character. Instead of just picking what class you wish them to play.
You can actually. It is a bit of a pain in the ass.
The basic method is this:
Open a new game>Make it multiplayer>Only accessible to LAN>Character screen (Don't finish yet, maybe you can. Haven't tried in awhile)
Alt tab to desktop. Navigate to your DOS 2 install directory. D:\SteamLibrary\steamapps\common\Divinity Original Sin 2\bin (this is mine) Now if your PC can handle it, open 3 more instances of the DoS 2 exe (EoCApp.exe)
In each of the 3 instances join a multiplayer game in LAN. It will usually be the name of your default profile. Choose the character you want to customize (not your main character), and proceed to customize it.
Now go back into your main character's instance of DOS 2, and finishing creating your character and begin the game. Now alt tab back into each of your other DOS 2 instances and finish creating your character and begin/join.
Once all 4 characters are in game, you can now exit the game in all but your main character's game. You now have 4 fully customized characters starting from level 1.