Story ID: PLEASE!!!!!!!!:)

Hi all.  Sorry to bother you but I have been trying for literally
years to identify this book I read as a kid.  I am 23, and I think I
read it btw. 8-13, so between 1988 and 1993.  It also might be part of
a series about the same characters.

Here's the story line:  There are two kids, a girl and boy, on
vacation with their parents to New England.  They are staying at a
Dutch mansion in New York that used to belong to the Stuyvesant
family.  The kids might be twins.  Anyway, they start seeing the ghost
of a young Native American woman.  They have to solve a mystery that
involves Henry Hudson and Baffin Bay.  An evil Stuyvesant male ghost
is also involved.  The twins are trying to right an ancient wrong to
the Indian girl, I think.  I feel like the book was blue and had a
picture of the ghost on the front, and it was paperback.  I have
searched on Amazon.com and on google and have found nothing.  Thanks
for your help!
Any new ideas for searching would be welcome too.

-Amy