Don't be mistaken, A Family Affair isn't a rom-com. It's a comedy about growing up, letting go and being yourself.
While the unplanned romance between her boss and her mother stirs plenty of emotions for Zara, our main character, she's a long way from being the grown up she believes she is. Instead she whines and wails about how eww and ick it all is, how horrible and blah blah to the point her best friend is ready to ditch her. All because the world stopped revolving around her.
The romance, her mother's first attempt to date since the death of her (not sainted, as it turns out) husband 11 years ago, is merely an inciting incident to Zara discovering that maybe she's got some maturing of her own to do, along with her boss, a movie star who's lived alone and in a cocoon of privilege since he arrived in Hollywood at the age of 19.
Fortunately for Zara, she has an intelligent, articulate mother and a hella intelligent, articulate grandmother to lean into and learn from. The acting is fine, the story is fine and there are some funny moments (I bet the writer who thought of the backstage scenes in Sleeping With The Enemy wished he'd been able to patent them - they're used in every film that has the slightest connection with drama, acting, plays or film). Enjoy, don't take seriously. The locations are all very nice :)