In my opinion it's very, very difficult for a 'third' to meet a couple for whom they share equal connection to both partners. I think it's important to allow each new 'couple' develop their relationship at it's own pace.
How are you meeting these new people? Who is making the initial contact with them and carrying on the conversation with them before you set your dates? If these women are primarily interacting with you, maybe they are just not as comfortable with Jeff as quickly as you and they hesitate at being with him because of it.
"Owning your feelings is basic to understanding the boundaries of where you end and the next person begins and the perfect first step toward self-acceptance and self-love." The Ethical Slut pg 69, Dossie Easton and Janet W Hardy
Scarlet's Blog: http://scarletsredletters.blogspot.com/