I’m pretty certain you can cross water without a boat. I’ve never used a boat for travel in the game to another area. I think if you get close enough to the shore, you can cross to an island. Try clicking on the water?
yeah i tried clicking on the water and on the land (where the mission site are). and the character stop on the halfway crossing.
its true that the brother can cross water but for not too far. if its going way too far from the land the party will stop like its blocked pathway