My impression: Barbie is not actually into this. She might find some of it appealing or arousing but overall, the idea of sharing or opening her relationship doesn't feel good to her. It sounds like you and Ken are struggling to refrain from expressing yourselves and acting on Your urges, but not out of respect for her, Just in hopes that she will come around. She can probably sense this and it might feel like pressure.
I say that there is a good chance that this will not really happen or go much further. I just get this feeling that you have decided all of a sudden that you want to fuck this guy and you don't really understand why that IS a big deal. Seems like Barbies concerns are more of an annoyance and obstacle for you than anything else.
l am not trying to be mean or rude. It's just what my overwhelming impression was reading your post. It's all about the sex...but a relationship is being tested and pushed over this...is it worth it? And what if Barbie decides she is just not with it and never will be? You sound like you might be the relentless type...