Im going through something similiar to this. Im running 5 screens total with one using dual USB and the other four being RCA. I havent decided on whoch VGA to RCA adapter to use so thats my question for you actually.
But to answer your Q I can tell you I was planning on running VGA to RCA and then run that RCA into a video amplifier that will supply four RCA video screens. They are pretty common on ebay.