I have beaten Wind Waker, finally! Great game, really enjoyed it

But I have a few questions I didn't understand, maybe I missed something, idk.
Spoilers ahead, I guess!
First one is, why exactly did Zelda turn in to Tetra again when she reached the surface? She is going up the sea as Zelda, but then comes out as Tetra... is there a reason for this? Did the King turn her in to Zelda? Or is this the "form" she takes in the land above? I don't really understand that...
Second, how did the King of Red Lions come to be? I know he's the actual King, but is this the "form" he takes when he's in the surface (a boat)? But then when he goes down to the land below, and he's still a boat...
And the last question is, if Hyrule was flooded, how exactly did the castle and Ganon's tower survive? Or is it that ALL of Hyrule below is still in tact? And is Zelda this King's daughter? We see a painting of her and all her crew, next to a painting of the King... But they never seem to show any hints of it when they're together... If he is the father, he doesn't show it much, imo... And if he isn't, how has he been alive for so long? Because from what I understood, the King we see is the one that was alive back when Hyrule was about to get flooded... but idk.
If anyone could answer there, I'd be very grateful! They're quite important facts, and idk how I missed them, but yeah...