2 Consoles, Same account, 1 GOLD Subscription

Each gamertag can only be signed in to one device at a time. If you are both using the same gamertag, one of you will get signed out when the other logs in.

You would need at least 2 subscriptions. With the Home setting, you can share gold on a console. So Account 1 would buy a gold subscription and set console 1 as their Home. Then they would use console 2. Another account would use console 1 and have access
to the gold. You would do the same with the other 2 console. https://support.xbox.com/en-US/games/game-setup/my-home-xbox

You would need at least 2 subscriptions for 3 consoles. You can only share gold on 1 console at a time, the Home console. So if you have Account 1, Account 2, and Account 3. Account 1 could have gold and sets Console 1 as it's Home console, all 3 accounts
can share gold on that console. Account 1 can then sign into any other console and still use gold because it's tied to that account. Account 2 or 3 would need to have gold and set one of the other consoles as their Home console in order to share gold on that
console. Then either of the 2 gold accounts can use the 3rd console.

Thanks for your reply. Do I understand that I will have to re-purchase content for simultaneous games on consoles 3 or enough to buy 2 Gold subscription as you described?

You would need at least 2 subscriptions for 3 consoles. You can only share gold on 1 console at a time, the Home console. So if you have Account 1, Account 2, and Account 3. Account 1 could have gold and sets Console 1 as it's Home console, all 3 accounts
can share gold on that console. Account 1 can then sign into any other console and still use gold because it's tied to that account. Account 2 or 3 would need to have gold and set one of the other consoles as their Home console in order to share gold on that
console. Then either of the 2 gold accounts can use the 3rd console.

Based on what you described earlier, Account 1 owns all the content. So, with that in consideration:

Anyone who signs into Xbox #1 can play any content that Account 1 owns and use its Gold subscription, even if Account 1 is signed in elsewhere.

When Account 1 is signed into Xbox #2, anyone can play that content or use that subscription, but if Account 1 signs into another console, even Xbox #1, that access on Xbox #2 is lost.

If Account 2 wants to be able to access Xbox Live Gold features, it will either need to (1) sign into Xbox #1 or (2) have its own Gold subscription on Xbox #2.