im not sure if you have resolved this but:
*just video: ONE RCA SPLITTER CABLE
* Audio and video: three RCA splitter cables off ebay
most units give out enough of a picture voltage for two screens... otherwise you may need a dedicated video amplifier/splitter...
(this one requires "more room" behind the unit... but what i would do is split it at the first headrest and take it across to the second headrest...)
if you splitting behind the unit though, go for this: http://www.ebay.co.uk/itm/RCA-PHONO-...item4cfe169ed0
--- if picture signal is too weak install one of these ;
NOTE: THESE ARE NOT THE CHEAPEST LINKS, JUST THE FIRST ONES THAT CAME UP! SEARCH EBAY AND THERE ARE CHEAPER ONES...
[DVD UNIT] ==RCA WIRE========================= SPLITER (1) ==PASSENGER SEAT===
(2) ======================= DRIVER SEAT=====