Saves on one xbox one not available on other xbox one in house / not cloud based saves

If you read the xbox support faq page the info is all there:

"Cloud saves let you play games on multiple consoles from where you left off. If you have more than one Xbox One console, or if you want to play games at a friend's house, you can store your saved games on Xbox Live servers in the cloud"

and

"On Xbox One, each game is provided storage. As a user's game library grows, so does their cloud storage, and an Xbox Live Gold subscription isn’t required. This gives Xbox One users unlimited cloud storage based on their library size"

To recap Cloud saves is storage for game saves and the space you got is based on the game you got.

Yes, any game saves created on the Xbox One will be saved to the cloud (once connected to the internet), and therefore will transfer to your next Xbox One console.

https://www.xbox.com/en-GB/xbox-one/backward-compatibility

"There are no Xbox achievements for Original Xbox games because this functionality was not available on the Original Xbox at that time of its release. Lastly, game saves will not transfer to Xbox One but once created on Xbox One, the game
saves can transfer to other Xbox One consoles through the cloud."

You'll need to copy/move your game saves from Xbox 360 to the
Xbox 360 Cloud-Based Saves. To do this, you must have an Xbox Live Gold subscription. Go to Settings -> System -> Storage -> Hard Drive -> [Name of Game] and select it. You should see game saves there. Select the one you wish to move and choose to move
it to Xbox 360 Cloud-Based Saves.

Next, launch the back-compatible game on Xbox One. When you start the game, it will prompt you for a save location; choose Cloud-Based Saves and it should bring in the file you moved to the cloud, letting you pick up where you left off. The save will be
updated when you finish on Xbox One, allowing you to return to Xbox 360 and continue again, or just keep playing on Xbox One.

Is your XBox One always connected to the internet when you are gaming? XBox One stores your saves in the cloud and if you are not connected to XBox Live you will lose progress that way since your last local synched save (which may not be up to date with
the cloud save) on your XBox One will only be available.

The Xbox One, Xbox One S & Project Scorpio all belong to the same family. So, all games will be compatible with the other two consoles and your saves will be available through Cloud storage.