Carly got pregnant to Lawrence as a young girl and gave birth to Nicky. Somehow Vivian paid the doctor to say he was stillborn and she raised him.
Through many twists and turns, the truth came out and Carly, Lawrence and little Nicky all left Salem together as a family.
While off-screen some years later, Carly and Lawrence had marital problems and she had an affair with Daniel at some medical conference, and got pregnant with Melanie (way before Daniel came to Salem). Lawrence knew he wasn't the baby's father and told Carly if she didn't give up Melanie for adoption, he'd have her killed, so Carly put her up for adoption.
Then even more years later, Carly and Lawrence were fighting (he was beating her) and she stabbed him in self defense, killing him. Vivian was out for blood and was determined to find that baby Carly gave up for adoption and kill her as revenge. (remember the poisoned hair comb she gave to Melanie at her wedding to Philip?)
Carly and Melanie "met" in Salem and eventually had a mother/daughter relationship (the show "teased" us as to who Carly's daughter was, Melanie or Mia). Later, Carly began doing drugs. Melanie came back to Salem to help with that, as did Nicholas (played by a new actor; they had de-aged the character). Carly, Nicholas and Melanie all left Salem together to go somewhere for Carly to go into rehab.
These are all "in a nutshell" descriptions of the basic storylines.
I know that the Salem family tree is really convoluted..... but could someone remind me of who Melanie and Nicky share?
Nicholas is an Alamain, so Vivian is his great-aunt. He's also a cousin to Quin, Stefan and Jake (Vivian's sons).
Melanie is a Jonas, so she's the half-sister of Parker and Holly. She's also Maggie's granddaughter, so Sarah is her biological aunt (Summer was her bio aunt, too). Melissa is also her aunt, but not biologically since Maggie and Mickey adopted Melissa. Melanie and Nathan Horton are cousins, but not blood related, since Melissa was adopted.
Frankie Brady is the full bio brother of Carly Manning, so he is the uncle of Nicholas and Melanie.