system
A chat on subreddit /r/pcmasterrace
human
What do you mean by "force the setting"?  
How does it work?  
Also I guess I could go for just freesync since they would all be using DP but... can g-sync and freesync work together for my main PC + side monitor?
gpt
I am at work now so i cannot be specific, but in the Nvidia control panel, G-sync settings, it will tell you that your monitor is not a supported G-sync monitor or something along this line but you can still enable it, that’s what I meant by forcing this setting.

As for your other question, i have an old rog gsync monitor as my 2nd one and I have been using such setup with no issues whatsoever.