The Olympus TG-4 is exactly the camera you should get - it has an easy learning curve before you get wet and is the best of the options available. The macro capability is awesome. As others have suggested the housing will allow you to attach wider angle lenses but I suggest you will get all you want from this little beauty without any add-on stuff. Like all small sensor units it can be a bit noisy (luminence noise) if you let it decide the ISO so I suggest using it in P mode with the iso set to 200 or 400 and if there is still noise then get rid of it in Lightroom or whatever you use.
Have fun the Maldives is a wonderful place and you will have the holiday of a lifetime - you can even learn to dive there!
I have a Sony NEX-5 body, Nauticam housing and tray that I could offer you if that set-up would interest. I have upgraded recently to Sony A6000 but had several happy and trouble free years with the NEX-5 set up. It is sitting on a shelf and I am sure we could agree a suitable price.