Amos' daughter Aseneth [Cousens] Emerson & family are living next door to Jeremiah & Eliza [Kimball] Cousens in the 1850 US Census. There are a couple other items to note in the Vital Records of Wells, Maine 1619-1950. Page 170 lists the marriage of Amos Cousens to Caroline Littlefield on 01 Jan 1808 and right below that is the marriage of a James Cousens and Hannah Webber. The day of this James' marriage is blank, but these two male Cousens, Amos & James, both married in Jan 1808 in Wells. This James Cousens' date of birth is confirmed in Vital Records of Wells, Maine 1619-1950 as 16 Dec 1784. So there's a possibility Amos & Jeremiah had a brother James, the son of your James born in 1756. Also, there is a notice of intention to marry on page 188 dated 09 Apr 1814 for Jeremiah Cousens and Ruth Bridges, both of Wells.