I want to make an active copy of my Gamertag for a friend aswell as making an active copy of his Gamertag for me so that we can log onto it at anytime and gain someone else an achievement or something similar without transferring the account and all that.

Basically two copies of each account and all four work actively.

I know this can be done but I want to know what I will need to do it and what I will need to do it. A tutorial would be appreciated if anyone has a link.

Thanks