I know of a great agent that will almost always get the best group rates. He loves what he does and will work with the largest consolidators to set up the most advantageous deals. Twenty families will involve alot and some great concessions. Contact him with some of your info and see what he can do. His name is Shack and he works for ITC at 877-635-0649.
Hope this helps,
He has saved my family great deals of money on vacations.