I'd use my biggest modifer directly behind and above the camera.
I'd use the rest of my lights and or mods to take care of the background or add accent lights if needed. If you're using a background I might consider throwing a gradient of light across it, or maybe use a bare flash with the dish to make a halo of light or something on the background.
If you want to do key/fill, you really need to work on positioniong people so they don't cast a shadow on anyone. I personally don't think key/fill looks good on group shots in most cases. If I do it, I keep the contrast ratio between key and fill pretty tight, and keep my key light closer to the axis of the camera than normal. I position it about 15 degrees off axis from the lens. Judging from your gear, I probably wouldn't do this though, you don't really have a modifier big enough to act as fill, and those small softboxes won't act as key on a large group.
I think your best bet would be to keep it simple. Use the Rotalux directly behind and above camera, use the 580 as a hair light and the other Eli as a background light to either cast a gradient of light on the background, or to make a halo of light on the background. There's probably going to be some color shift between the Elis and the 580. It would be less noticeable if the odd light out was used as a hair light.