1) Does your computer have TV-Out? if so go to 3.
2) Get a VGA splitter, plug one VGA output to the touchscreen, one VGA output to a VGA-TV converter
3) plugin the TV-output from the converter/PC to a Video Y-splitter cable and run one AV to each of your headrests.
Beware that the quality of the image on these screens (unless they are VGA, which I doubt they are due to their price) will be basically useless for reading any text... good enough for videos/games though...
Good luck and post pics! that seller is well known and I suppose is pretty trustworthy