Why is him wrong?
The "he" is the subject of the sentence. "him" is an object pronoun.
His own. He's a time traveller.
He's no son, he's no son of mine. XD
Maybe he is one of those kids that get lost in the beach.
"Who's son is he?" Is wrong, should it be?
It's incorrect :), the word you're looking for is 'whose'. They're often confused because they sound the same when you say it out loud. I hope this helped you