I have been asked to photograph some family group shots on a staircase at Luton Hoo
. You can get a rough idea of the staircase and the surroundings from this picture....
not my image
I've never been to the place and as it's 50 miles away I won't get to see it until the day. I don't know what sort of lighting they have there, or how daylight might factor in, depending on weather, sun position etc etc.. The shoot is between 12:40 and 13:15. I understand that the room curves around behind the camera position with a continuation of the off-white walls, so lots of potential for bouncing flash.
The patriarch and matriarch want all shots to be taken with people posed at the bottom of the stairs, using the bottom five steps only, so there will be no need for shifting lights around (I hope). There will be various arrangements of people from a minimum of two up to a maximum of 21.
I'll be shooting with a 5D2 and 24-70 on a tripod and I have 2 X 580EX with stands and the option of brollies if it would help. I can trigger wirelessly in manual flash mode. I'm going to have no time to set up and experiment beforehand because I am also a member of the family group, expected to appear in one of the photos, and we're just taking 35 minutes out for the photos. For the rest of the day I'll be hobnobbing and stuffing my face. 
I'm hoping for some help with figuring out how best to light the group for maximum appeal. Should I just bounce both flashes off the wall behind me? Would it be better to use the brollies, and as shoot through or reflective? Should I stick one of the flash guns behind the group for hair/separation, and should I fire directly at them or bounce off the wall behind them, more like a background light? I have almost zero experience with off camera flash, or shooting formal groups, so I don't know what would work best given the limited time, resources and experience. I'd be grateful for any suggestions. Thanks.
BTW, I've only found one image on the internet with EXIF to help me out and the image there for a large group was taken with a 5D at 40mm, f/4, 400 ISO, 1/2" plus flash.
not my image
p.s. Is this the kind of shot for which I'd be better off shooting from a stepladder (which would mean no tripod, and also a problem for the largest shot of all, in which I am to appear)?
