Anyone here who has the game know if Companions can level up as well? If so, is it automatic or do you have some control over it?

bump

anyone there?

nope, If they do however, you have nothing to say anout it.
They do have theyre special little talents, and you can tell them to do certain things.

hope that helps!

Are Companions useful to have around if you have a 'Sneak' character? Or do they give away your position?

If you go to sneak mode, so will your companion.
And I think the companion levels with you, sometimes they can even be better then you.