[mcgregni]

It's the dome style diffusers, turning the flashhead into a 'bulb,' which creates the wide even spread. For portraits where directional light and contrast is nice then it's not the right thing, for wider spaces and group shots it can work, even a single flash with lightsphere.

I'd say probably the softbox is not much help here, as it contains the spread of light and is likely to lead to uneven light in a room. The Stofen diffuser is sort of the right idea, but they are not large enough to throw the light sideways enough, with still a lot of forward light straight from the flashhead.

[Canada_Rockies]

I did some Christmas family photos and used the camera flash as a trigger together with two manual flashes into 30" (80 cm) umbrellas at 45 degrees left and right, about 10' (3 m) from the subjects. I got nice even lighting. I used my ancient flash meter to ensure that the umbrellas were even by firing them one at a time with the push button, and checked the output from the camera flash as producing nice in eye highlights without blowing out with the direct flash. I think I had the K10 set to use minimum fill flash on camera. I have also used my AF 540 flash as a trigger on minimum manual, but that's another thing to tote around.

[Class A]

Yes, this is not a matter of timing, just of level control and creating soft light.

This is a situation where Stofen-type diffusers can actually help. But potentially such diffusers would need flagging in order to avoid direct lighting and the respective shadows.

You should be successful by just bouncing your flashes. Don't point them to the subject wall directly but fire them into the opposite wall, in order to create huge virtual light sources that should give you shadowless illumination.

If the backwall is not suitable for bouncing light off it then use the side walls, and/or room corners. Just create big secondary light sources and you shouldn't be able to see any shadows.