You will need to go with one of the bigger companies to insure the right mix of boats are available. Any of the companies will be glad to help you arrange everything. You should be able to negotiate a nice discount with a multi boat booking. I have done a bunch of these in the past and I provide two cautions. First everyone thinks it’s a great idea and wants to go until you call and ask for money. Second if you have 30 people going you will get 29 ideas on the perfect dates. I once no kidding had someone call and tell me two weeks prior to sailing that we needed to move the event back two days because something came up. They were quite upset when I explained there were 23 other people going and the boats and airfares were locked in. Hearding cats can be a good description for these type events. Once you set sail they can however be fantastic!
G