There's one fully-written scene with the XO, with more to come (eventually). For the procedural stuff penetration should be allowed if the genitalia and orifices match up, but there's hundreds of potential combos so I can't rule out that some positions might have incorrect cases. If none of them work you may be clicking on the wrong participant or such (or you might not have given them the right genitals).
Viewing post in Carnal Voyages - Public Release Version comments
Okay, I might need a walkthrough, please. Here's exactly what I encountered. My character has a vagina, XO has a penis. I chose doggy position with mine as the bottom. From there, what would the exact steps be to see penetration happen? Because I couldn't request him to do anything with is penis. If he was already penetrating, the game didn't really make that clear.