It really depends on what each instance is configured for, If you have an instance that requires a lot of resources and it is critical that it does not get affected by other applications using up those resources then obviously a dedicated instance per machine makes sense. One instance per machine also makes it easier to manage as you do not have to change default network ports or add additional networks to accommodate two instances.
However, there are one or two reasons why running two instances on one machine may be beneficial. For example, a common scenario is that you can test multiple server deployments on a single server before rolling them out. We do have the following article explaining how you can configure a single server to run separate Wowza installations simultaneously, though do note that it was written when Wowza Media Server (not Streaming Engine) was the current product,
So do please be aware of the implications regarding licensing (you will need a separate license for each instance), and ensuring there are no conflicts regarding network ports. Also note that although most of these ports can be configured via the Streaming Engine Manager UI, the Manager UI port itself is configured within the [wowza-install-path]/manager/bin/startup.(bat or sh) script file.
If this is aimed for production though, you will probably be looking for the easiest to manage and least complex Wowza setup, and in that scenario, I would generally recommend installing one Wowza instance on each server.
One other option to consider would be to “Dockerize” those instances on a single server:
Please let us know if you have any questions.
Technical Support Supervisor