Sounds super easy and is. I'm just here to let you know a few things...
you can get this by playing with any other profile on your xbox, it does not have to be gold or anything. you just can't play with a guest.
you only need to play with 1 other person, not "friends", just a "friend".
To get set up just go to Challenges.. select the level and difficulty and with your other controller press X to join and sign in and you are ready to go.
and if for some reason you haven't found this site yet...
http://www.familyfeudinfo.com/