Does godson have to be spelled with a capital G?

No, "godson" is not a proper noun, so it does not need to be capitalized.

It is a common noun referring to a person who is the spiritual son of a godfather.

Here's why you don't capitalize it:

* Not a specific person: "Godson" refers to a general concept, not a specific individual.

* Not a title: While "godfather" can sometimes be used as a title, "godson" is not.

Therefore, you would typically write "godson" in lowercase.