I have just been asked to take photographs of four couples (two of the couples feature my kids) around 5pm today. I plan on using a 5d3 (or my 60D), a 430X flash and plan on using a Sigma 35 1.4 along with a Canon 70-200 2.8IS II.

I mostly photograph baseball, birds and nature, I take lousy people photos and almost never use flash. I typically shoot with auto iso and use manual shutter speed and f stop. These photos will be outdoor on my front lawn, in the backround there will be plenty of shrubs, a few flowers and a red maple. The house will block the sun that will be starting to set in the back yard. I can also go to the backyard where there is more sun and a white six foot tall fence if that is a better setup.

I assume that I should use flash as the subject will be in the shade (house will block direct sun). Should I mount the flash on the camera, if not where? Which lens do you prefer for full body portraits and what camera (and flash) settings do you suggest? I realize that this is last minute and not so easy to get great photos without decent gear and much more knowledge than I have.

Any advise is appreciated.

Thank you,
Scott