Hi Kris,
Thanks so much for visiting the Disney Parks Moms Panel with your questions.
The
Pirate Adventure Cruises look like so much fun! On these cruises, little scallywags can depart on one of four adventures to find treasure. The adventures depart from Disney's Grand Floridian Resort & Spa, Disney's Caribbean Beach Resort, Disney's Yacht & Beach Club Resort, and Disney's Port Orleans - Riverside. Each adventure is a little bit different, so do follow the link earlier in this answer to read about the adventures and chose which would be best for your boys. If you think that they will enjoy any of the adventures, you might choose the adventure departing out of Disney's Grand Floridian Resort & Spa simply because it will be the closest to Bay Lake Tower at Disney's Contemporary Resort.
I am not sure as to the limit on the number of children on each ship, but it is not too many. It also may vary by adventure, so I suggest that you ask that question for the specific adventure you choose at the time of booking. As to the snack, it is listed as a snack, such as a pretzels and juice, so I would not count on it being their lunch. When you are ready to book an adventure for your little pirates, call 407-WDW-PLAY (407-939-7529).
I would like to thank my fellow Disney Parks Moms Panelists Kirsten and Kimberly for their thoughts on this answer. Have a wonderful time planning your trip, Kris, and please do not hesitate to ask if you have any further questions!