I'll start simple and wait for the requests. I'll just be doing some of the main characters, unless somebody requests otherwise.
Carlos - He's a Bottom person, mainly due to his lack in strength. He will want Top once or twice in a long-time relationship, just to know how it feels, but he generally sticks to Bottom.
Jay - Always Top. Being a very dominant person, and very strong, it's easy for him to take dominance over his partner. He likes to be in control, so Top is his go-to.
Mal - she prefers Top, and dominance, but she will take Bottom on the off chance that she feels like being submissive, generally if she's had a tiring day, or is just stressed.
Evie - She's a switch, not minding either. It depends on her partner and how she feels. If she's having a smooth, stress-free day, she'll be happy to take Bottom and let her partner take control, whereas if she's been rushed and feels things are spiralling out of her control, she'll take Top, as it'll give her control in something in her life.
Ben - He's a switch, changing to suit his partners needs, although it depends a lot on his mood and energy. If he's been pent up the whole day and has a bad case of Cabin-Fever, he'll take Top. If he's tired, he'll take Bottom. If he's relaxed and chill, he'll really take whatever his partner wants, although he prefers Bottom there.