Vivian Alamain is Lawrence's aunt. Next to her, Kate looks like Rebecca of Sunnybrook Farm.
Vivian connived a way to have Kate & Victor's embryo (Philip) implanted in her. (She had a thing for Victor and freaked out when he married Kate.) So, she is not Philip's biological mother (Kate is) but she is the 'birth mother'.
She buried Carly alive, in an elaborate scheme that would've made Stefano proud.
She kidnapped Nicholas and made Carly and Lawrence think he died at birth. They were all reunited several years later -around the time of the burial fiasco (Carly was saved by Lawrence) Vivian had Nicholas in a private boarding school.
Carly chose Lawrence over Bo and they rode off into the sunset with Nicholas.
Now she's back!
Carly was Bo's fiance. He got involved with her when Hope was presumed dead. She had a relationship with Victor as well. (Can't remember the details)
Rafe probably told Daniel because he's a doctor, knew where the baby was and could decipher the DNA results to know Rafe was being truthful about Sami being Sydney's mother.
I wonder where they are going with the Carly/Mia/Vivian storyline. Oh, God, I hope Vivian doesn't sink her claws into that poor young girl. Vivian is the personification of evil.