SOLVED. YA/ Middle grade, 2 book series, 4-5 kids spending vacation at a castle without their parents. [s]

[Janelle E Clark]

Looking for a 2 book series I read multiple times mid-90s. Got from a church library (books have since been cycled out), so they were Christian based. It was 4 or 5 kids staying at a castle on vacation without their parents, they did solve a mystery each book I think? One of the books had an artist, possibly a professor (maybe both, one in each book?) staying in the castle but was very unsociable. I do remember at one point they knocked on his door and there was a “Hello?” And they started talking to him through the door but were interrupted by “I’m busy, come back later” or something to that effect - at some point they figured out it was a recording that was triggered by the knock. One of the kids hid inside a suit of armor at one point to try to overhear clues to what was going on.
The only other thing I really remember is there were secret passages and one of them came out underneath a waterfall.

[Rainbowheart]

The Secret Treasure and Trapped in the Secret Passage

[Janelle E Clark]

!!!!!! Yes! Thank you!!!

[Rainbowheart]

No prob, glad to help out!