Modern Warfare 2 asking for Xbox live but I have it already

My son primarily uses his console and I use the other one. Can gold be used on both consoles under this same account or does each console need a gold account for online pay?

We have two consoles at our house. By making his console my accounts "home" will that mess up our other consoles online play access?

The games you listed do not require Gold to play online so he would be able to play those without your subscription. Make sure you have the console set as your Home console to share the Gold with him. https://support.xbox.com/en-US/help/hardware-network/console/my-home-xbox

The Gold is tied to the account, not the console. So the person who owns the Gold can sign into any console and use the Gold. If you set your son's console as your Home, he will be able to access your Gold, then you can sign in and use your console and still access your Gold.

It depends on how your setup is and how many people are using your consoles. You can only have 1 console set as your Home at a time. So if you have multiple people using your current Home console and you change it, then they will lose access to your Gold on that console. If it's just you, you'll still be able to use the Gold since it's tied to your account.