Can I assign two mice to two windows or have two pointers?

I figured out how to put two pointers at the same time and control them with two mice (using xinput), but can I have them both assigned to a window? Since I can only have one window in focus I can't use both of the pointers properly because one will be on the focused window and the other one won't. I'm trying to play a LAN game with a friend and, if this is possible, we'll be able to play in split-screen. I have a second monitor available, but if possible I'd prefer it on one screen. I'm also trying to avoid emulation since I have an older PC with Ubuntu. I'm new to Linux so it would be nice if you could explain every step.