If I have two discs for Minecraft on the XBOX, will it get confused?

The disc only contains information to run the games. The saves are kept separately (i.e. are not stored on the disc, but in external storage), and belong to each user. So if you had 2 copies of the game, it would make no difference to your setup.

So in other words, Bob signs into his profile. He plays Minecraft. He creates his owns worlds, plays his own games etc. When Bob's finished, John signs into his own profile. He has his own worlds, and has no access to any of Bob's worlds, unless they play split screen - together.

To clarify, split screen allows players to play on the same console, but there will be a "primary" account, and the other (up to 3 others) will be the "secondary" accounts. In this situation, the "primary" account is the one that started the game. The players will then be using the save games of that "primary" account.

Splitscreen is a Console Edition-exclusive feature that allows up to four players to play on one screen at the same time.

Source

So all in all, getting a separate copy of the game will have no effect at all.

there is a splitscreen version but if you only want one person to play at once, it would work. To settle any confusion you can create 2 seperate accounts on the xbox's memory unit (whichever one you use) and they cant possibly see each others worlds

so basically with two seperate profiles the disc is useless.