Using Lightroom on multiple computers

Your original post does not say anything about how you will be using Lightroom.

LR is designed as a single-computer, single-user system. If you want to share files and editing between multiple computers, there are hoops you need to jump through to trick LR into getting this to work.

You can install the software on all three machines but only two can be activated (signed-in) at any one time.

You can use LR on 2 computers with One License whether that be a Perpetual, Stand Alone, license or the Subscription base CC version.

It can be used on both Windows and Mac at the same time. One computer being Windows and the other being a Mac. It doesn't matter what OS you are running on the 2 separate computers.

Where the limit comes in is both computer shouldn't be, can't be by the terms of the license, used at the same time and the same person should be the primary user of both computers.

It's Lightroom 6 and it's an online version.