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And have you actually considered just using good old-fashioned rotoscoping - by hand using masks and what have you? Sorry, but I don't even know what tracking has anything to do with anything here - unless you really mean using mocha Pro or other advanced tools. The rest is merely you looking for simple solutions. Yes, roto work is tedious, but sometimes unavoidable. There isn't a magic button for everything.
You are not approaching your problem rationally. The tip of the nose and the bridge of the nose don't move when someone is speaking. That's what you track. You could also use the corners of the eyes. Now the face is locked in the frame and you mask around the mouth. Trying to track the entire mouth can be done but not with the tools that come with After Effects. Given proper photography you may be able to track and roto the mouth and lips in Mocha but it would take some preparation and some careful camera work. Even using Mocha, you would want to Stabilize the shot first using parts of the face that don't move.
Once you have the face stabilized, not tracked but stabilized, then you can either choose s soft edge mask and use makeup to blend the surrounding area of the mouth with the other shot, rotoscope the edges of the mouth to get a tighter mask, or use makeup and keying to cut out just the mouth and lips.