Modern Greek γιος is similar to Ancient Greek υἱός. Is γιος descendant from υἱός?
Yes, of course. ^.^ (Νot to be confused with the word ιός, which is a translation to "virus" xD).
υιός is also the Katharevousa form of son. I think it's still used occasionally in set phrases such as "άσωτος υιός", prodigal son.
The root is also in υιοθετώ "to adopt", which I don't think is ever written γιοθετώ.
Yes it could, but keep in mind that the pronoun is not necessary. Mostly because each verb has its own form. Αυτός is used for a bit more emphasis, translating to this.
However, you might notice that the pronouns are used in several skills, for the sake of teaching. ^.^
I did choose the answer correctly from the word bank, but afterwards I was left with the question of whether you can translate this as, “he is my son”. If not, what would be different about the sentence?