[clackers]

if you are doing fill flash outdoors you really wouldnt want to use a diffuser right? i like using something to diffuse(piece of paper probably wouldnt work well in your scenario so maybe a diffuser cover) indoors

You're always looking to go large with a diffuser. The bigger the softbox or flash bender, the softer the light.

In direct sun with HSS the flash might be so weak in comparison the 'bare bulb' might be needed.

[slip]

I am with a different school of thought. I would take the 16-50 for groups and full body couples. I would take the second body with me and have the 85 for upper body couples (or you can back up and do full body shots)
Shade is your friend.. try to find some with a nice simple background if possible.
One thing I learned is kids don't care how technically good your photos are, they just want to see which ever they look best in (I don't know how many times I showed my kids photos and they liked the ones that to me where unsharp) and posted them on facebook!
Oh one more thing, if possible if you are doing small groups or even couples try to keep their faces on the same plane so that everyone is in focus. Don't worry about beautiful bokeh as most people are not concerned about that... only photographers worry about that

Good luck and post some results