We started ripping up the carpet and noticed the subfloor is not level in the living room to the hallway. There are 2 layers of lenolium in the hallway that will need to be ripped up. What can we do to level the subfloor?

Being "level" and "flat" are two different specs. Flatness within manuf.spec is what your after. Over concrete ...it's a matter of grinding high areas, and filling low areas. Over a wood subfloor....there's different methods, depending on the situation.

Is it a sub floor or is it an underlayment over a sub floor? How many layers, composition, and joist spacing first of all. The we'll work on the two layers of linoleum.