why do you use Lunus? I have Luna, Lunae, first declination...
if they are going to say "lunus" as you suggest, then they won't be thinking of the Moon, they will be thinking of something else... But you are right in the sense that Luna, as a name, would be a feminine name; but the boy's name is "born of the moon", so the full name should be something like "natus ex luna" -- the masculine would be in "natus" because that's the part that refers to the boy; Luna is a feminine name and it should be used the right way if you are meaning the Earth's satellite, or at least that's what I thought the OP wanted the misunderstanding to be (between the dying man and the others).
And yes, domum redi means return home, the preposition (ad) can be omitted.
It's the most commonly used with that meaning, just google domum redit (present) or domum rediit (past).
The verb, redire, is irregular, and if you are looking for "may he return home", it should (please check!) be "domum redeat".