Battlestar Galactica - Last Supper

I tried to pixelate this poster: http://www.syfy.com.au/sites/syfy.com.au/files/show/images/battlestar_galactica_s4_-_1.jpg

I aimed at having a "point & click" adventure style and I ended up with this mess :) Backgrounds are difficult (even though I took all the help I could get from Photoshop), characters double so and I am convinced the facial impressions are almost impossible. I am trying to find out a style that works in all cases, as professional pixel artists do. I just don't know where to begin. I could not put a single pixel on this one, without the reference photo on the first layer. So I beg for advices, comments, critics, anything that could help. Should I keep practising with reference photos? Or am I already doing it wrong?