I'd reconsider using a bare bulb. Shooting groups (it would help if you could say how large the groups are expected to be) with a bare bulb is going to give you harsh, deep, shadows and glaring highlights, more so if the walls and ceilings are relatively dark... Consequently, depending on how you set up the shot, you may find that the shadow cast by one group member will obscure another and that the fall off from the foremost subject to the furthest will be rapid. In short, bare bulb will be unflattering to your subjects.

If you can't get hold of brollies and more powerful strobes, I'd suggest you fire both flashes (with reflectors) backwards at a larger reflector, behind and above you, to get the required spread. I use an old sheet of Tyvek that I keep in my kit for this, if I haven't got my fold out reflectors with me. However, guide numbers won't help you with this set up, you'll need a flash meter. I wouldn't risk doing this type of thing without one, especially if I was shooting film.

However you go about it, you need to diffuse/reflect those lights to soften the output...