SOLVED. Juv/YA - Twins, eccentric family, hall of mirrors, indian prince [s]

[Mel]

Here is one that I vaguely remember from my childhood but haven't been able to find. It involves an eccentric family with the youngest being twins (boy/girl I think) who are particularly talented - smart maybe something more supernatural. I also remember some mystery about an indian prince? And a hall of mirrors that was the key to solving the mystery and saving the prince. It definitely had aspects of magic.

As a warning I have been known to meld book plots in my head so it is possible the hall of mirrors was from something else. Pretty sure the twins and the indian prince went together though. Read it in the early 80s most likely. I get stuck on "Octagon House" when I think about it so I probably read them both around the same time, it definitely isn't "Octagon House" though.

[Emily]

Could it be The Diamond in the Window?

[Mel]

Yes! Thanks for that. Never realized it was part of a series, may have to go back and read them all.