Thoughts on how to approach a high number of automated parallel tests

I work for a small company that uses Java and Selenium to write scripts for automated testing. They simply use google chrome browser to navigate the web page and enroll a user into a website. We currently have 7 computers, each of which are running 2 instances of this script so each computer is enrolling 2 users at the same time.

I added testNg to the project and now we can run any number of parallel tests that we need, each running the test for a different user but the problem is, that is a lot of CPU power needed to run more than 2. With testNg, it looks like we can run around 5 with no issue but we want to be able to run a lot like say 20 at once. The program crashes if we try that as expected.

I’m wondering should we abandon the testNG addition to the project and go another route? Or what else can we do to run these scripts? Doesn’t matter if it’s headless or not.

Edit: also we don’t need to see the scripts run or have any logs. We create the logs ourselves as the scripts run.

Thanks!