Parallel launch of applications in xvfb, how to organize it correctly?

Question

linux

Good day everyone.
I've come across a situation where I need to launch multiple console applications that require windows.
I implement this through xvfb with the following script:

#!/bin/bash
DEBUG=*  /usr/bin/xvfb-run --auto-servernum --server-num=1 --server-args="-screen 0 1024x768x24"  /usr/bin/node --harmony /home/user/projects/project-name/worker.js

The question is, when you try to run several scripts in parallel, the server is busy and unable to connect.
Logically, I understand that a virtual X server rises in the environment, to the display of which applications are connected. I just can't understand why each application needs its own window. And how to be so as not to write differently screen 0 screen 1 and so on.