large group family session...help??

[nicnelly]

I am still quite a newbie and although I have gotten pretty comfortable with single person portraits with natural light I need lots of help to get to the next level. I have been asked to do a family session for a group of 20-25 people about 1 1/2 hours before sunset. I am willing to rent/buy the equipment I need to do this correctly. I will buy if I can afford it and I think it will work well in the future (planning to continue with children/seniors....maybe some day weddings?) but rent if it isn't a priority for these situations.

I shoot with a Canon 50D and I have a 50mm 1.4 and an old kit lens (18-55mm) and a tripod. I know I need to invest in more lenses and lighting but I'm not sure what should come first.

So specifically....best lens for this size group and best lighting suggestions? If this is the wrong area to post please let me know! thanks in advance!