There is one more child of Isaac and Harriet not on your list, whose relations I have been in contact with, Margaret Philbrook Norton and her son Ken.
David Philbrook, died in 1914. He is buried in Lanesville, MA. He was married on Oct 28 1884 to Ellen (Nellie) Howard.She was the adopted daughter of Albert Howard and Mary Hanscomb. (Ellen was reportedly a Blackfoot Indian)
David was probably the oldest child and was not living with them in the 1880 census. (We need to check 1870)
Isaac and Harriet were married 14 Jun 1860, in St. George, Knox, Maine. They also lived in Pigeon Cove/Rockport, Essex, Mass.
Also, Isaac's year of birth is listed as 1832 on his grave stone.
I believe the date of 1833 may have been miscalculated from a census record taken before his birthday, but I haven't confirmed this yet.
This is a copy of an email "cousin" Ken sent me:
It's always fun to hear from a distant cousin!Since I sent you the email, my aunt produced a copy of Isaac's obituary that lists all of the children(including Amber).The copy is in pretty bad shape and no one can remember the date or the citation (we think it was the Gloucester Times).I am working to get a cleaner, verified version.But here is some info from it:
It states that Isaac T. Philbrook had 13 children, 3 of which are deceased. The list is 6 boys and four girls: David [my great-grandfather], William,Isaac Jr.,Ernest,Arthur, and Harry, Lillian, Annie, Susie and Amber. "Mr.Philbrook left Pigeon Cove in 1901 moving to Rockport, Me., where he resided until the death of his wife in 1910, then lived with his children ... He sustained a broken hip a short time ago from which he never got much better and which was the immediate cause of his death."Then it goes on to say that burial will be in West Rockport cemetery.
end of letter.....
Nancy died in 1909, so the obit must have been wrong.