@perrero Imo he would do okay with grandma and SIL based on your replies, but I would likely take mine with.
While he may not mind and even enjoy his stay with grandma, I disagree about not remembering, I was in the US (half US half European) before I turned 2 and I still have memories from it, plus ofc the pictures and everyone else's stories to fill the stuff I don't remember.
Anyways, kids
do remember and even if they don't cool stuff like this will make them proud/happy especially later on (since galapago island sea is pretty much equally cool as a small downtown lake for a toddler), but at the same time safety is a reasonable issue and the kid will do fine without you, so it all boils down on what
you want to do.