I'm not sure what you know of them, but I've found out a little more about Grace and Leonora Porter's ancestry in the twelve years since I posted my inquiry.
Their parents were Samuel Porter, about whom I have nothing, and Eleanor Brothers, b. about 1837, possibly in Quebec, and d. 5 Dec 1883 Sciota, Clinton Co., NY.
Eleanor's parents were:
Edward Louis Brothers (Edouard Louis Brodeur)
b. about 1810 in Quebec, d. 28 Aug 1883 in Chazy, Clinton Co.
Married 9 Nov 1824
Lucy Gonyea (Lucie Gagnier)
b. Oct 1811 in Quebec
d. 26 Jan 1907 West Chazy, Clinton Co.
They had lots of kids and apparently came south following the uprising in the late 1830s.
I took some of this info from a post by Ronnie Brothers Dec. 29, 2001, on the Gonyea Forum at genealogy.com
You may want to search the names of your grandparents at the Northern New York Newspapers site http://news.nnyln.net/
You'll find a sweet story about your grandparents' wedding among other bits.
Let me know if you want any other info about them.