1) On N. Royshoma Coast how do you get into Oni Island or The Land of ..

Well, there's a particular order to what you have to do. Firstly, you need the technique Catwalk, which can be aqquired by climbing the large tower on an island in the North coast. (please note you will need to have met the messenger of the Dragonian Kingdom and gained the ability to ride on him)
Once you have done that, you need to go to the first island you see in the coast when you enter. If you don't know which on that is, it's the really large one that stands beside the restaurant. Use the Catwalk ability to climb to the top, and speak to the man who tells you about seeing a shooting star and then, once he's seen one that you create by putting an ink dot in the sky, he'll talk about the whirlpool galaxy. At night, go down to the bottom of that same island, and from there the game is self explanitory. The messenger of the Dragonians will exclaim you found the entrance to their kingdom, and by getting on him and swimming into the whirlpool you can get to the land of Dragonians. The game is self explanitory from there.