The film will be directed by Garry Marshall and also stars Jack Whitehall, Aasif Mandvi and Loni Love.
Olyphant, 47, plays Henry, the ex-husband of Sandy (Aniston), according to The Hollywood.
Mitchell, 28, portrays Henry's beautiful new wife who wants nothing more than to be the perfect stepmom to Henry and Sandy's children.
Robertson, 25, stars as Kristin, a slightly neurotic new mother to a one-year-old girl. Whitehall plays Zack, an aspiring stand-up comedian and Kristin's boyfriend.
More From This Section
Wayne Rice, Mike Karz, Daniel Diamond and Brandt Andersen are producing with the script penned by Anya Kochoff-Romano, Lily Hollander, Matt Walker and Tom Hines.
The movie began filming in Atlanta last week and is due to open in the US on April 29, 2016.
Olyphant was a series regular on FX's series "Justified", which ended its run after six seasons last April.
Robertson's latest romantic movie credit was "The Longest Ride", in which she starred opposite Scott Eastwood. Mitchell stars on hit series "Pretty Little Liars", which is currently airing its sixth season.