well it mostly depends on what "age" are you wanting to emulate but it can be done
if you aim for dos games, i guess that dosbox can do it just fine, one problem would be sound routing to each corresponding headphone, and the fact that only one can use keyboard and mouse
if you aim for newer, windows based games, then you should consider using an hypervisor, then add the corresponding cards needed and run two windows instances at once, each with it's own soundcard, videocard and ethernet card, the limit is, however, that you may end using 6 PCI slots and still you will be lacking keyboard and mouse support on one machine

there's a Linus Tech Tips video in where they use a workstation/server class machine with XEN i think, and two video cards, so they can use that machine like if it where two of them, but the price for such a thing can be really high

I have built such a thing, not for the same reasons, and there are variables.

I use qemu-kvm with vfio passed hardware. The specifics of motherboards will allow/disallow things depending on details you can't really figure out until you try the hardware. Everything depends on how the IOMMU groups work out. On larger Xeon server boards this usually works out well. On lesser things shortcuts taken can affect the available configurations, regardless of how many slots and usb ports you have. Older pci-e lanes from chipsets, pch, mhc, and the like are often easier to route than cpu provided lanes. Available lanes change according to whats plugged in, you can run out of lanes...

Generally, a single hdmi/dp video card passes sound and video entirely independent of the host. Host doesn't necessarily need it's own card, or can use onboard. USB may enumerate into 3 or 4 groups, each passable to a vm for keyboard and controllers. That may physically make sense on how they are laid out, maybe not. Save a slot for an extra eth card to pass, this help certain things like vnc control from the host. Some 2 port cards will group into two ports, one per machine. Four ports so far I only see 2x2, I'm still looking for a four port that groups 1x4.

So sound and control can be isolated. There are no focus issues. 2 or 3 people can work on one machine and never know they're sharing. Twice in the last year I've had the host interface lock (nvidia+xfce) while a vm was recording tv and working in another with no effect. When done I came in from another machine and cleanly restarted the host, that's independent proof right there...