Check to see if this set-up is even viable. An EC cannot just bring in volunteers to do work they have to be bonafide employees under lincesee supervision. I'm not sure how that applies in charitable situations, so check. If it were me, and I do plenty of work at my church, I would make sure that I could supervise or I don't know that I would partake. My church may be a little different because everybody knows what I do, so they understand that it would be my undertaking. It sounds like you have a much larger project going on. I agree with the statement earlier that if you are clear of liablitiy, help where you can and let the GC handle the responsiblity. Do what you can to make it safe and "assist" others where they may be in error. If church leadership is counting on you to make sure it is right because they know you and your qualifications, have a sit down with them and the GC to clear up the roles of all parties. Design issues, where you are concerned about adequete lighting in some areas, are a whole separate nut to crack. It sounds like issues that have already been decided and laid out. Outside of suggesting change orders there may not be that much you can do.