I bet that right now, they have hard time imagining what a sea of change they are going to face in a few months. I can think of no better gift for a lover than your time when it is most needed - even taking the baby for a walk so that the new mum can take a short nap can be a life-saver. So the lack of enthusiasm is just part hormones and part of Gina having no idea how their life is going to change.
As to Davis - I'd wonder too if you will be able to give him the time and energy he needs, especially with this baby thing. On the other hand, it seems he is not going anywhere as it is. Have you talked about what being primaries might mean both for you and him and for you and Gina and Eric and baby Giric?
Me: bi female in my twenties