Have your tried Synergy for your mouse/keyboard situation? Another possibility is perhaps a KVM switch that if you plug in two outputs into the same computer that it is recognized as two distinct USB devices. I don't know if it's possible but then you could pass through one to the VM directly.
Synergy is decidedly non-optimal for gaming, unfortunately. Various games try to grab the mouse pointer in different ways and synergy throws a wrench into at least some of them.
since switching to VM based gaming about 6 months ago I've played and completed: SC2 LOTV, Bioshock Infinite, Crysis 1/2, and The Talos Principle and have not had a single problem.
