Facial animation, unless you use facial mocap, and characters engineered to -use- that kind of data, is still the province of manual keyframing, just as posing hands/fingers and feet/toes are. Unless you can find someone who has done it and released it, your best bet is to find a kissing scene in a video that you like, capture it, do a frame by frame step, and copy it. And be prepared to create some custom morphs, or do some work with magnets of the morph brush.....