https://www.linkedin.com/in/reuben-sack-600a49a/
You have to log in to see his page. He also wrote "A Nancy Drew Christmas", which had Frank and Joe appear in it.
Edit:
https://www.linkedin.com/in/cathy-hapka-a8a08113/
Another ghostwriter, altough not sure for what series. " Author/creator of several other original titles/series. Writer for many popular series and licenses: Nancy Drew, Hardy Boys, The Saddle Club, Romantic Comedies, Sweet Valley, National Treasure, Winnie the Pooh, Curious George, and more. Experience in all age groups."
Edit 2:
https://www.linkedin.com/in/paul-crilley-0117b020/?locale=de_DE
Wrote "Curse of the Ancient Emerald."
Appearently S and S has stopped caring about wither ghostwriters reveal their identities.
Know this is an old topic. but I have an update
Reuben Sack also wrote:
Sea Life Secrets
A Treacherous Tide
Return to Black Bear Mountain
Dungeons & Detectives
https://images.app.goo.gl/acbJPvurJA8zPsJh7