Naiad and gnome family question

Ok so, I have some wierd questions. I'm in a campaign that's about to end, and my character, a male (ish, nb but thats beside the point) ranger gnome got kinda engaged at one point in the adventure with a Naiad, the thing is, since we're near the end, I was thinking on what he's going to do after our mission ends (if he doesn't die) and I'd like for them to get married and live together and at some point have children, but I'm not sure how that would work since they're different species and naiads are made of water, so I'm not even sure if she can be touched without passing though her like a ghost lol. In any case, they can adopt and I'd be happy either way, I just want to know if having a biological child is a possibility for character design purposes. Also from what i know from Greek mythology nymphs can't be away from the body of water or plant they're attached to, but I don't know if that also applies to dnd.