The pair previously held the roles of creative director and head of planning at Craik Jones Watson Mitchell Voelkel, before the agency was merged into Proximity last year.
They will now be responsible for helping to grow Joshua's brand response offering, working on brands such as Allianz, Nestlé, Procter & Gamble and Nickelodeon.
During their time at Craik Jones, Rae and Parkes were responsible for creating a number of award-winning campaigns, for clients including Gordon's Gin, First Direct and Refuge.
Nick Hoadley, the managing director of Joshua G2, said: "Rebecca and Caroline are both heavyweight talents within their respective disciplines, but as a team they bring the driving force behind Craik Jones' great work.
"They are both relishing the challenge and the opportunity that Joshua G2 brings."