group photo

[Choet]

I will be doing my first wedding in August (Winter) for a friend who is aware that I am an amateur photographer. I have been madly reading up and practicing photo taking on friends and family. I have hit one problem that I don't think that I can fix. My friend wants the family photos taken inside the church. Apparently the church isn't a very well lit church. I own a Pentax K20D, and a Sigma Ef-530 DG Super flash, plus 50mm f/1.4, 18-55mm kit lens, and a 24-70mm f/2.8. All of my research so far indicates that I couldn't successfully take photos with the limited equipment that I have. I can't afford to hire extra lights (plus I wouldn't really know how to use them). I have always used bounce flash, haven't as yet bought anything like a Stofen Omni-bounce (not that I am sure that would help me for this situation anyway). The setup I have is fine for one person, couples, and really small groups, but I am not sure it would be enough for lighting family photos in a dimly lit room. Would I be correct in assuming this?