Ask HN: Setup for 3 Laptops

You could also take a look at https://symless.com/synergy or something similar (I think there's an open source version too).

I assume you've already considered ssh-ing into them from one "master" machine?

I tried several solutions but recently purchased a LevelOne Tech KVM. Best solution I've found thus far (albeit a little pricey).

https://store.level1techs.com/?category=Hardware

Find the 4 port option which works best for you (single or dual display). This thing has been bulletproof so far.