2 games, 1 console

Not sure if youre talking digital download or physical disc.

Are they both disc based, or digital copies? There should be no issue. The install will stay the same, if it's disc based, it'll just verify that the disc is in the console, and play from whats installed. Shouldn't have any issues. If they are mix-matched
(digital/disc) I've seen a few issues of it asking for a disc when it's owned digitally, but that's not common.

There's no issue with this, but why not just buy a copy for your house and have him leave the other at his mom's? Seems easier for everyone that way!

Hey Timbo

Thank you for taking the time to post this on the Xbox Forums. We understand that you are currently inquiring about using differ copies of the same game on your console.

As stated above by the other Xbox Forums Ambassadors, this will not cause a problem. If you son owns this digitally, he does not need a disc to play it since he owns it [was bought under his account].

Unless the Xbox is configured as the
Home Xbox, you will be required to either have a physical copy of the game, or be signed into the same account that purchased that game in order to launch it.

As far as save data goes, as long as you are connected to the Xbox Live [the internet] you will be able to

sync up your save data from everywhere, once you log into your personal account. There will not need to be a fear of overwriting the wrong data as long as you are signed in correctly.

Additionally, if you are planning on picking up where you left off on another console, its good practice to

close the game or app before you head over to that over console.

I hope this was able to clear up any confusion or turmoil this might have caused.

Ah ok ty ... so basically for example...i want to get watchdogs... i want to play it on my account on my xbox ..my son says .. oh good i can play it to now on mine u dont need to buy me one now ... ?? Wud i lose my place in game if he used it on his account
his console?? Sorry for acting so dumb .. im a xbox virgin ..lol ..my son n bf has got me into the xbox so once i get one nxt month .. i b playing watchings skyrim n assasins creed ... i dont have many friends would u mind if i added u as a friend im not
on xbox yet but soon will b and looking fir more online friends to help me along wiv my xbox fix lol all help is appreiciated