The book "Sibley Family in America" by James S. Sibley names Ann Flint as Isaac's wife. Other places name Ann Atherton as his wife. Personally I do not know which is correct, as I've never been able to find anything on either of these two women. I wish I had access to James Sibley's book on the Sibleys as maybe he has listed his source there for claiming Ann Flint as Isaac's wife.
Also I would like to see a copy of Isaac Sibley's will probated in Savannah Georgia on 24 Dec 1810 Effingham County. Would you have a copy of it?
If you would like to compare notes on Isaac and his family, contact me off-line at Dwedgewort@aol.com.