If I can be of help? We live within two/three hours of Gettysburg, Lancaster, and Hershey. We have been to all three areas-most especially Lancaster. My take on trip possibilities:
Disclaimer-I am trying to be objective (okay, trying)
#1-Hershey- a nice enough park. Naturally, not a Disney, and not as nice as Dollywood. If my main reason to come on this trip was to go to Hershey, I would suck it up and stay at the Hershey Park Campground. That extra hour in the park (that camping at the Hershey Campground gives you) makes all of the difference when it come to getting on rides. We went camping with our church youth group here, and by noon the lines were long, long, long. Like why am I even here long. If you are not a big amusement park enthusiast-I wouldn't even go to Hershey. There is also the Hershey Museum here, a tour of a fake Hershey candy factory, and some outlets.
#2-Gettysburg-I have been here twice. A truly interesting place to visit. If you are in the area-go. HOWEVER, (again, my opinion) you only really need one day here. Maybe two if you are a huge Civil War enthusiast. When we went, we visited the museum and visitor center and toured the battlefield and listened to a few ranger talks, and a day was enough. I believe there are some nice campgrounds in the area.
#3-Lancaster-my favorite of the three. There are the Amish and fantastic let's put on five pounds places to eat. Not anything WOW to do, but a fair amount of little things. The Strasburg Railroad, outlets, Amish buggy rides, bus tours that take you to Amish houses where you can eat and mingle with the Amish, tours that let you semi-mingle with the Amish, and Shady Maple (look it up-you will be captivated-trust me).
So, I am thinking that the group needs to prioritize what are the most important things they want to do and go from there.
Hope this helps,
Kathy