Well, to start ... my experience is that you have to invite couples to dinner parties otherwise things become a little unbalanced, so with this in mind, my couples would be:
Josephine Baker (20's jazz singer/dancer) + Richard Burton (the Victorian explorer/linguist/libertine not the overrated actor/husband of Liz Taylor). As they both had a pretty liberated attitude to all things sexual (and were hugely talented) I think they would make a pretty good pairing and add little pizzazz to proceedings. I'd have loved for Dick Burton to have made an appearance in the Demi-Monde but unfortunately Philip Jose Farmer had first dibs on him.
Marilyn Monroe + Cyrano de Bergerac. In my humble Marilyn was the greatest comedy actress of all time and Cyrano was, of course, a freewheeling genius. A match made in heaven.
Jane Austen + H.G. Wells. Jane could explain to me how to write in third-person omniscient (which I don't get) and Herbert could explain to me what it's like to be the greatest SF writer of all time (and maybe give me some plot ideas).
Eleanor de Aquitaine (a real feminist!) + John Henry 'Doc' Holliday: I wanted both of them to feature in the Demi-Monde but in the end they got squeezed out. These are two people in history who I admire because thay had the force of character to be their own people.
Billie Holiday + Charlie Parker. Okay the drugs might be a problem but the jam session after the meal would be unreal. The thought of Kit duetting with Charlie and Nelli harmonising with Billie with Ellie on bass ... far out!
Marguerita Zelle (aka Mata Hari) and Francis Walsingham (Elizabeth I's spymaster). They could sit in a dark corner and exchange encrypted billet doux. Hopefully Marguerita could be persuaded to dance. Now she and Josephine Baker tripping the light fantastic would make for an interesting evening. Zowie!!!!
Top that line up, folks!