Goodreads Librarians Group discussion

Marsha Forchuk Skrypuch is the author. She has written two different series set in WW2. The books are currently sharing a series page, under the series title "WW2". I don't think either ha an "official" series title, but it's not uncommon for series to be named after the first book - that would be an option for differentiating the two.

The first series is three books:
1) Stolen Girl
2) Making Bombs for Hitler
3) The War Below.

Second series is:
1) Don't tell the Nazis
2) Trapped in Hitler's Web
3) Traitors among us

Done

The fact that these are two separate trilogies is confirmed by the author's website.
According to GR rules: "If no series name is available, please check author or publishers' sites to see if a series name has been allocated. If there isn't one, Librarians can either use the main character's name or the name of the original book."

Two series, named after the first book have been created.