Hi,
I forgot to mention an important point on my setup:
User Peter is in a chroot, while user Tom is not (on the main host, where the chroot is running).
In a X2go session, I can use the same display when I do a xhost + and set the DISPLAY variable for the second user to the same as first user, but when I do that for the chroot user Peter, to be able to use Toms display, it does not work. What special steps are required to make this possible for chroot? I tried to install x2goserver in the chroot, set the port for ssh to 23, but I cannot log in that way to Peter.