My physical copy of Modern Warfare 2 for the Xbox One had issue in starting and said that...

I have an Xbox one and bought the physical copy of modern warfare 2 and it will not install

You do not understand the issue, you have to understand that there is modern warfare (not free) and modern warfare war zone (free)

For those who have a physical version, we can't access the original modern warfare campaign and other stuff from the main game that we purchased, we can only access modern warfare war zone, everytime we try to play the original modern warfare and not modern
warfare war zone it tell us that we have to purchase it. Even though we had paid for the physical version already.

There are Two Xbox ones on my network and only one can access Xbox live servers for Modern Warfare at once. One will get on just fine then the other one will keep failing to connect to Xbox live servers until the other console gets off. What can
be done for this?

Do you 2 copies of Modern Warfare and a separate gold account for each console?

We have two Xbox's and we play fine online and with Modern Warfare.

It's the decision of the publisher if they will allow the game on game pass or not. In this case it's Activision. Whether they would allow it on there is anyone's guess.

You can purchase Modern Warfare 2 & 3 from the Xbox store here
https://marketplace.xbox.com/en-GB/Product/Modern-Warfare-2/66acd000-77fe-1000-9115-d80241560817 & here

https://marketplace.xbox.com/en-GB/Product/Modern-Warfare-3/66acd000-77fe-1000-9115-d802415608cb

You might also find physical copies from your local or online game retailer.

I'm assuming you're referring to the Modern Warfare beta access issues hit Xbox One
players. I only had the message "too early to start playing" the day before the Beta. I had no issues playing the Beta all the way up until it ended and I ranked out at level
30 which is all they allowed.