My initial reaction is don't. POV or POVs should be consistent throughout the book. I can see the reviews- I thought the book was about Mary but all of a sudden it's all about Joan for three chapters and then back to Mary. What the...
Now something like an event, a bbq, where Joan and Mary have a conversation and later in the other series the same conversation takes place from Joan's point of view, just don't make the repetitiveness too long, then it's okay.
I just read a book by Sarah Pekkanen and there were four main characters and it was constantly flipping between their points of view for a couple of pages at time and it was fine.
Example - Emily Giffin, her books, Something borrowed and the follow up told the same story from each character's point of view, then she had another book where the woman, was Dex's (one of the characters from Something borrowed) sister. I didn't explain that very well, but it was fun to see Dex referenced in the new book.
Edit - Make the town your brand - A Misty Hollow Romance - Mary and John series, Joan and Bobby series, etc.