Brothers being what they are. My brother was impressed with my new HM100 and (having more $$ than I) decided to get one. Now during family gatherings he wants both of cameras in action. Is there a way to sync the two cameras time codes easily for editing?

Yes. Set the cameras side by side, turn them on and get out your IR remote to navigate the menus.

Go to the TC/UB menu, set TC GENE. to "FREE" RUN, then go up to TC PRESET and set whatever TC you want. I suggest using the current time of day (in 24 hour clock format).
At the moment you hit the "set" button on the IR remote both cameras will be running "time of day" free run TC and be in very close sync.

Should have been able to figure that one out myself! Duh!

Easy, use Pluraleyes. PluralEyes (http://www.singularsoftware.com/autosync/)

Even easier, start both cameras recording, take out your mobile phone, point it at the running cams and take a shot, (make sure the flash is set on). place clips in trimmer window or on the timeline and cut to the flash, it will be one frame. Job done.