Families are "we" and have always been "we."
When my mother-in-law had cancer and my wife told her that "we will get through this together", my mother-in-law didn't respond by saying: "The biological reality is that only I individually have cancer. Don't give me this 'we' nonsense."
No, she realized that her cancer not only represented a serious psychological blow to her but also to those who loved her and that the people who loved her were suffering as well and that they would do anything in their power to help her get well. My mother-in-law told me that she feared the devastation that her death would have on her husband and children more than she feared dying itself. That makes complete sense to me.
Likewise, a pregnancy is a time of hope and expectation for everyone who loves that child, and those who love the child are willing to do anything in their power and endure any discomfort to help ensure that mother and child emerge from the pregnancy healthy and happy.
The notion that the only reality is physical is not a traditional notion at all - it is the diametrical opposite of traditional morality.
A family is not a bunch of random people. It is an entity itself.
Yes, he was excited, worried, nervous, and we shared those feelings. So was my mother. She wasn't pregnant either.
Tradition has long observed that only women are pregnant, however connected the father and other family and friens are to the event. A couple claiming that "we" are pregnant is defying reality, and asking us to play along. It's bogus and a bit emasculating, not to mention vaguely insulting to the woman who bears the baby and labors to bring it into the world, in my opinion.