I remember when I used to play arcade games that allowed both players to share keyboard. Bomberman, Golden Axe, Double Dragon, etc. Here is a list of co-op games https://en.wikipedia.org/wiki/List_of_cooperative_video_games
Now you have controllers as well, where you can connect multiple Xbox or PS controllers to an USB hub and onto your computer and play without space restrictions.
By default I bound the keyboard like this:
1. Kil - W,A,S,D and SPACE
2. Mil - Arrows and RCTRL
This proved difficult for me to play along with my kid so I will have to play around with more options.
Here is the full video log: