Y/A fiction, 18th century Massachusetts

I read it in German translation in the early seventies, so probably published in the late sixties. I believe it was based on fact, about a settlement called Stockton/Stockbridge/Stockport, two main characters (brother and sister?) named Erastus and Elizabeth. Can anyone help with this?

I think this is Elizabeth George Speare's The Prospering, based on the life of John Sergeant who was a missionary to the Mohicans in Stockbridge. Elizabeth is the main character and Erastus is her sister's son.

WorldCat seems to indicate the the German translation was called "Die Chronik von Stockbridge."

Yes, that's it! Thank you so much!