Complex sentence: Ultimately, the father realizes that he loves his son if he is a Martian, or is not, and the son uses a magical "Martian wish" to be a human so he can remain with his father.
Split into simpler sentences: Ultimately, the father realizes that he loves his son, whether he is a Martian, or not. The son uses a magical "Martian wish" to be a human so he can remain with his father.