Honestly I'm not a fan of any abusive type relationships. Or even in the later phases when it's not abusive it's still not my favorite. I personally see them as brothers, and the age gap is the same age gap as 2D and Noodle, 12 years.
I do kinda like Russel x Murdoc, mainly all my shipping fuel...
I like being Mabel because she's literally me in so many ways, I kin her but I also just love her. But I wouldn't actually mind for this fandom. I usually don't like to play males but Theo is a very interesting character to write in my opinion so I really wouldn't mind either way. I love them both