Oh well Neptune is Poseidons Roman counterpart right? We decided it best to not include the whole Roman/Greek thing as it would confuse to many people :/ so any lore and otherwise in those books will most likely be left out.
Hmmm I'm not totally sure about Artemes, she's not entirely focused on in Percy Jackson and I don't have very much outside knowledge of her, I was planning on having her children born in the same way as Athenas but I'm not sure how that would work.... but I dunno, I'll leave her in for now and see what happens