Let's see, trying to think back. I read 'The Arrangement' a couple months ago. The main character is definitely Natalie, a struggling artist who gets roped into this insane 'marriage of convenience' deal to pay off her mom's medical debts. The guy she marries is Tom Faraday, the super rich, closed-off CEO who proposes the whole thing. His motivations are... vague for a long time, which is part of the plot.
Then there's Natalie's best friend, Chloe, who's constantly giving her terrible but well-meaning advice. Tom's assistant, Mark, is like his eyes and ears, always hovering. I think the only family member really in the mix is Tom's younger sister, Amelia, who's sweet and seems to suspect their marriage isn't real. Oh, and the obligatory ex-fiancée, Serena, who shows up to cause drama halfway through. Honestly, Serena felt a bit like a plot device more than a full character.