You need to have the HM whirlpool which I belive you get from the 7th or 8th gym leader in Johto
You use it to summon lugia at the wirlpool caves.BUT YOU NEED ALL BADGES TO SUMMON HIM WHICH I TRIED BUT I NOTICED I ONLY HAVE 7 WITH MY LEVEL 30 POKEMON.
you can't get to any of the Sevi island in Pokemon Heartgold and soul silver
the top left
i have no clue
The Cinnabar Island
cindber island
it's impossible
Seafoam island is in the Kanto region in Heartgold and Soulsilver.
East of Cinninbar Island and southeast of Fucshia City.
You can't. New Moon island is in Sinnoh.
I believe the Top Right island.
You can find it on Cinnabar Island.