You probably already have a boat, because it's the first thing you need for this journey.
My parents and I noticed our catamaran was perfect for this journey. When sailing we could leave our stuff on the table without falling on the ground. Since we could use the table in all weather conditions, we could entertain ourselves easily. A monohull is limited in that way. Keep this in mind with the preparations.
Make sure there is a little spot in the boat for the children and parents so they have a small space for themselves. Sometimes you need some space without someone else standing in your way.