Hmmmm… It seems the main problem will be to show all 3 galleries together in one “masonry grid” 
Other than that, Part with the galleries I would make from the Tabs widget and add each gallery to the separate tab pane. Masonry grid can be easy done by following this post:
Once again, 3 galleries together put in one masonry grid will be hard, since each of them will be wrapped in a div (Dynamic item)