Headcanons for how they are in bed:
Dennis: He definitely has a praise!kink, and is surprisingly submissive. He's watched how people have sex and has obsessed over women for years, but is more comfortable letting you take the lead and telling him what to do. He is worried about being too rough with you. His favorite part of your body is your legs, he never imagined he'd get to touch them, let alone have you guide his hands to your thighs.
Barry: There's lots of giggling and moaning, and there would be an equal balance between submissive/dominant. He's had sex before but never had a girlfriend, so really getting to know someone and what they like is thrilling for him. He'll figure out exactly what does you in, and likes to pay extra attention to your lower back and the dimples there after learning what it does to you.
Jade: She is a dominant one, so when she wants something she will tell you exactly what she wants you to do with a flirty smile and a promise that it'll be good for you too. She is all about foreplay, getting the both of you worked up before she's even really started. Her favorite part of you is your ass, and she never misses and opportunity to tell you.
Patricia: She is dominant, but in a more subtle way than Jade. She will gently guide you to where she wants you to be with a firm hand, watching you with predacious eyes and giving quiet whispery instructions on what she wants you to do. Her favorite part of you is surprisingly your ankles, after she grabbed you by them and slowly pulled you to the end of the bed and felt the delicate bones there, she loves how you twitch when her touch tickles you a bit.
Orwell: He is pretty chatty in bed and easily the most talkative. He tends to be submissive and has had little to no actual experience with sex. His favorite part of you is your lips, when you're kissing his neck it's one of the only times he can't think straight enough to talk.
Luke: He thinks of himself as a proper ladies man and is rather cocky about it. He's dominant but not extremely controlling, he knows what he wants and how to get it with lots of sweet talking in your ear in his southern accent. Your neck is his favorite part of you. He loves hugging you from behind and nudging your head until it tilts to the side so he can kiss and rub his stubble on your neck and whisper in your ear.
(I'm not adding Hedwig for obvious reasons, and I didn't particularly have any headcanons about the other personalities I haven't already listed.)