Cynthia Sirk has handled social media marketing for a decade, and her clients are five locally owned restaurants in rural Maryland: two Mexican, one Central American, one Chinese, one seafood. Almost every customer lives within 30 miles. Three of the restaurants run a weekly special, so every Monday she collects the details, builds the flyers, and schedules posts across the week. She works mainly on Facebook, because in a small rural area everybody is there.
The thing she will not compromise on is that each restaurant keeps its own look. A family Mexican place and a Chinese kitchen are not selling the same evening, so she picks a different template for each and tailors it rather than using what is on the page as-is. When she is building for Cinco de Mayo she passes over anything that does not suit a family restaurant, looking instead for a sombrero or a margarita pitcher if the promotion is on margaritas. Then she deletes what does not apply, adds the promotion details, the website, and the restaurant's own logo. She designs the menus herself too, and it is all just her.
You can set each page up the same way. Size the artwork properly with Facebook cover templates, give each brand its own saved palette and logo in Brand Kits so the covers never blur into each other, and build the matching weekly specials from restaurant templates. One Monday then covers every page you run.