One is fed from the PC, the other is fed from the Macbook Pro, which is sitting on top of the PC, where its own screen is not really that usable. My primary computer in the home has a small desk, with a 32' Samsung HDTV monitor and PC keyboard. BTW a Bluetooth Mac keyboard works for almost everything on a PC that has Bluetooth also. Not that this particular Mac has a broken screen, so I have to keep it in clamshell mode (closed) for the external monitor to work. I am using a PC keyboard, which works fine for almost all Apple purposes (with the exception of screen print, which it can't duplicate), but a USB wired Apple keyboard would likely be better for your purpose. Nice things about this: I have only one monitor (a 32' Samsung HDTV) on the desktop, a single keyboard, and single mouse. Two position switches are also available. I am using this four position KVM switch Amazon link to switch Then you connect the video output from each Mac using an adapter to HDMI. The second (and the way that I have setup my shop, which has three PCs and the Macbook Air 2 of the PCs are Windows 10, one is Linux Mint Cinnamon 20) is to connect an external monitor, keyboard, and mouse to a good all HDMI KVM switch. Every machine I have can be accessed with this, because TeamViewer is available for Windows, Mac OS, and Linux. This works well for intermittent access (such as accessing my Macbook Air located in the shop from either a PC or Mac inside the house, but is not ideal for full time use on two machines side-by-side. When you finish, shut down the connection. Install on each Mac, remember the 'partner ID' for whichever you don't have a keyboard/mouse on, change the access password from the default if desired (this is a separate password from the Apple ID), and access the second from the first.

One way (for non-commercial users, commercial costs $) is to use TeamViewer. There are a number of ways to accomplish this.

Mac pc share keyboard mouse