The Secret of the Terror Castle is the first title in this series.
Here is the US Version:
01 the Secret of Terror Castle Us
Here is the UK Version:
01 the Secret of Terror Castle UK
Let me know if you have issues reading the PDFs...
I loved reading these books and wanted to share what I have found on the Internet so far. Email me if you find any more stories having Jupiter Jones, Pete Crenshaw & Bob Andrews. Have fun.