Genlock two OV5642 camera modules on Arduino with ArduCam
Looking at the User Guide, it looks like pin 8 on the "alternative connector" is the trigger input. I assume if you drive a 3.3V active-high signal into the trigger pins on your two modules, they'd fire at (relatively) the same time.

However, I don't see anything on ArduCam's web site to indicate this thing is capable of shooting streams of video -- and I don't know how fast you can shoot still photos. They're basically using a CPLD to read out the DVP's data, buffer it a bit, and shove it on the SD card. No idea how fast it is.