Susan and Carol

Carol Willick and Susan Bunch are Ross's lesbian ex-wife and her partner. Carol tells Ross that she is pregnant with his child in "The One with the Sonogram at the End" and is having it with her partner Susan.
Susan does not attempt to hide her contempt of Ross and vice versa, but they briefly put aside their differences in "The One with the Birth" when Carol gives birth to a boy, Ben. Carol and Susan get married in "The One with the Lesbian Wedding".

Here we have an example about how their relatioship works between Ross and Susan.
ROSS: So, um- so how's this, uh, how's this gonna work? Y'know, with us? Y'know, when, like, important decisions have to be made?
CAROL: Give me a 'for instance'.
ROSS: Well, uh, uh, I don't know, okay, okay, how about with the, uh, with the baby's name?
CAROL: Marlon
ROSS: Marlon?!
CAROL: if it's a boy, Minnie if it's a girl.
ROSS: ...as in Mouse?
CAROL: As in my grandmother.
ROSS: Still, you... you say Minnie, you hear Mouse. Um, how about, um.. how about Julia?
SUSAN: We agreed on Minnie.
ROSS: 'S'funny, um, uh, we agreed we'd spend the rest of our lives together. Things change!

(...)

SUSAN: Oh, please! What's wrong with Helen?
ROSS: Helen Geller? I don't think so.
CAROL: Hello? It's not gonna be Helen Geller.
ROSS: Thank you!
CAROL: No, I mean it's not Geller.
ROSS: What, it's gonna be Helen Willick?
CAROL: No, actually, um, we talked about Helen Willick-Bunch.
ROSS: Well, wait a minute, wha... why is she in the title?
SUSAN: It's my baby too.
ROSS: Oh, 's'funny, really? Um, I don't remember you making any sperm.
SUSAN: Yeah, and we all know what a challenge that is!
CAROL: All right, you two, stop it!
ROSS: No no no, she gets a credit, hey, I'm in there too.
CAROL: Ross. You're not actually suggesting Helen Willick-Bunch-Geller? 'Cause I think that borders on child abuse.
ROSS: Of course not, I'm... suggesting Geller-Willick-Bunch.
SUSAN: Oh, no, nonononono, you see what he's doing? He knows no-one's gonna say all those names, so they'll wind up calling her Geller, then he gets his way!
ROSS: My way?! You-you think this is my way? Believe me, of all the ways I ever imagined this moment in my life being, this is not my way!
DOCTOR (entering): Knock knock! How are we today? Any nausea?
ALL: Yeah. Yeah. A little.

And here's a video with some UNSEEN SCENES with Carol, Susan, Ross and Ben.