How do I get the basketball?

It looks like it's stuck up there.  You'll need to shake it loose.

Try throwing something at it.

Throw the stone at the ball and it will come down (F).

Now you need to recover the ball from the little boy.

Have you noticed that all of the houses are interconnected?

You should also notice that each goblin goes through a slightly different
pattern when he walks through the houses.  So try both goblins and see where
they end up going.