You've met the Harpers (Jake and Kari from Trusting in Faith), but you haven't met their grown-up children. Kyle and Emerald are twins, born in TIF. The Lees start with a standalone as well, but these two families join together in later stories, which are WIP and TBA.

While I don't mark these books as their own series, I do have a recommended reading order for this section of books. But you can still read them as standalones in the bigger series. The reason this is the recommended reading order is because of the age transition of the characters.

Trusting in Faith: The Harpers #1 -

Kari and Jake are 16-19/20 in this book.

Aaron and Cece's book (Title TBD): The Lees #1 -

Aaron and Cece (Cecelia) are 16.

Her Jasper: The Harpers #2; The Lees #2 -

Jake/Kari's daughter Emmy, Aaron/Cece's son Jasper. They are 15-17.

His Rose: The Lees #3 -

Aaron/Cece's daughter, Rose. She is 15-17.

Kyle's Book (Title TBD): The Harper's #3 -

Jake/Kari's son, Kyle. He and Aria are 15-17.