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Please see the official X‑Plane Support page for help.
I am not with Laminar Research; just a flight simmer.
I am not in the position to advise on how and what to do to get a system like you intend to be operational but I offer information you need to consider further.
Firstly, if you intend to run a copy of X-Plane on more than one computer at the same time then you need a Licensed copy of X-Plane for each PC. I understand a silent or secret check is made when X-Plane runs to determine the validity of your copy.
X-Plane is designed to run in 1920 x 1080 screen configuration. Others have run 4K screens but you need to carry out a configuration within X-Plane to be able to view the screen either by "magnification" or very large screen(s). You may get some benefit from the following link found at https://www.youtube.com/watch?v=CUjuQDKS-6s and produced by Michael Brown. Michael builds PCs predominantly for X-Plane. Laminar Research recommends his business as the "sole" supplier of PCs in the USA suitable for X-Plane. Michael has now "dumped" the projector system and recommends large size televisions screens for the multiple screen view. The multiple view system is setup within X-Plane.
The latest version of X-Plane ie V11 is very resource hungry. More so than XP10. Have a look at the system requirements found at https://www.x-plane.com/kb/x-plane-11-system-requirements/ Many serious flight simmers build a purpose built PC equal to or of greater specifications than the recommended specs. Although X-Plane is developed on a Mac system, Laminar Research recommends building a windows based system for best benefit. If your 5 old PCs don't meet the specifications don't even contemplate using them. What is not mentioned is good cooling. Cooling is required as heat is generated in both the GPU and the CPU.
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