Interesting question, actually thought on this lately for The Sisters. From left-most to right: Erin, Beatrice (job/nightwear), Jam, Scott, Connor, Sammy, Craig, Handsome Dan, PB, K.C., Conrad.
I sort of hear Erin as sounding like April Winchell in her normal speaking voice, like back when she was doing her podcast. Sort of calm, rational, and collected; but only because if she isn't holding it all in it'd be a complete mess. All contained, all measured, and a bit rough and masculine as befitting her.
For Beatrice, I like Katie Aselton. Her voice, her natural voice, has this sort of falseness to it. Like there's a hollow sing-songy quality, like she's hiding something and she's just putting on a big face. Maybe mix in a bit of the roughness of Michaela Dietz or when Aselton starts to lose her voice.
Jam's always sounded like a chav that somehow ended up in Boston to me. Energy but not energy that wants to be expended, sarcastic but only because she knows it bugs you, vulgar for the sake of vulgarity. Not a butch voice, or one that's too girly. Sort of a Helga G. Pataki kind of voice, riddled with confidence and a sense of self that most people twice her age would give their left nut to have.
I like Scott as a Donal Logue type, during his earlier years. Kind of tired, knowing, maybe a slight caustic frustration that seeps in but ultimately someone whose just been dealing with crap for years and has made his bed in it because that's life. The kind of voice that can teach math, talk theory, and that would belong to a guy you'd assume to be a dad by this point in life.
Connor would sound sort of like Walton Goggins doing a slightly deeper voice. No accent, just a sort of confidence and knowing voice. Someone who is having fun with what he's doing.
Sammy is hard to place. Take a metal head from high school, the one who is fat and has long hair and lacks a lot of self-worth, and that's sort of how he'd sound. Easily excited about things going on that are worthy of excitement, but really kind of fed up with brother Craig.
Craig is Zak Bagans. That's the whole of his character. Maybe throw a bit more dude-bro in there is at all possible. Push that dude-bro to the point that the hyphen in dude-bro is gone forever.
Handsome Dan would sound like Michael Raymond-James, if he thought he sounded like Colin Donnell. With some David Rasche in there when he gets frustrated, or is trying to sound like a way cooler cop. He'd channel that Sledge Hammer something fierce.
PB would be something complex. Riddled with defeat, a bit of self-loathing like the kind you hear from a depressed friend who is pretending not to be depressed so you don't feel bad, compounded with someone who isn't getting their hormone therapy as often as she'd like. Someone so done with it that her life feels done with it. The kind of voice that when happy, you know it is richly earned---because happiness is such a luxury.
K.C. won't be back for a good long time, but I sort of hear him as a more gruff Fred Willard. One of his previous designs was a bit more like Willard. K.C. should sound like the kind of man who could coach little league without making the kids feel bad.
And lastly, Conrad, would sound a little like Walton Goggins doing a Michael Cera impersonation. Spineless, maybe a touch of smarm there, someone who isn't enjoying what they do but does enjoy what it is they can do.
Probably something like that.