I think the Ellery Manchester who married Abby King is NOT the son of John & Nancy. However, I am still researching this family.
This entry in the RI Cemetery Database has Ellery dying in 1841: MANCHESTER, Ellery 1802c - 1 May 1841 PV001. If this is accurate, he can not be the one who married Abby, because they are in the 1850 & 1860 censuses. The year of birth for Abby's husband seems to be c1807 or 1808, from the census data. If he is not the son of this couple, whose son is he? (This needs more research.)