This is an interesting thread.
I have to give Greg "Rock DJ" by Robbie Williams, just for the fact that I can totally see him dancing to this one, and actually have this stray Robbie Williams track on his playlist. Aside from that, there's also Silverchair's "Abuse Me", in particular the chorus lines "Come on, abuse me more, I like it." I think he'd enjoy singing that line out loud.
I'm giving Nicky "Life is a Highway" by Tom Petty, "Tougher than the Rest" by Bruce Springsteen ("Around here baby, I've learned you get what you can get, if you're rough enough for love, Honey I'm tougher than the rest. Well, the road is dark, and it's a thin thin line, but I want you to know I'd walk it for you anytime..."), "The Joker" by The Steve Miller Band ("Some people call me a space cowboy, some call me the gangster of love...") and "If she wants me" by Belle & Sebastian ("If I could do just one near perfect thing I'd be happy...Things fall apart, I don't know why we bother at all But life is good and It's always worth living at least for a while..."). The first two, I can see him playing in the car and singing along.
Sara, now, I give her "Least Complicated" by the Indigo Girls, it sounds a lot like her. "Brown Eyed Girl" by Van Morrison and "Absolutely Cuckoo" by The Magnetic Fields also works, the lyrics really capture that magnetism she has:
"Don't fall in love with me yet, We only recently met
True I'm in love with you but you might decide I'm a nut
Give me a week or two to go absolutely cuckoo
Then, when you see your error,
Then, you can flee in terror
Like everybody else does
I only tell you this cause I'm easy to get rid of
but not if you fall in love..."
I'll leave everyone else for later.
It took a lot out of me to think about this.