Church records might be your best bet. Have you zeroed in on a location within Franklin County for the Lowells?
Where have you found them in any censuses, and did they have any children?
Many marriage repertoires exist, even some for baptisms, for Franklin and other northern NY counties' parishes. Have you tried asking the advice of the NNYACGS library, which has many such repertoires?
Even if a couple lived in Franklin County, they may have returned to Canada to marry, or to have their children baptized.
We do not have time now to check if our Israel Boyer / Boyea had any sisters, but will put that on our list for the new year...
Best of luck,
Tom & Barb Glassel