Hey there!
So the general technique is to go out with each of the pair twice, to get an idea of what they want. You'll then have a 'think about Xs problem' option in the bedroom, with the duo option if you've gotten both to that point. Every character you can go out with has usually one potential character they can pair up with (Samantha being an exception, with two. She also needs a few extra days and talking to her after your second date. Mason is also an exception, he just needs his persona quest complete and not paired with you as a dominant or submissive). Looking at your list
Damien and Xun can pair up
Samantha and Mason can pair up
Cass needs Siren Petra
Petra Dark elf needs Vampiric Xavier
Masked Jolie needs electronic Cassy
Sara, Nadia, and Michael do not have pair options.