I looked in my database and did not find anything that could help you with your Joseph Seaver who came to Watertown NY and had children, including the son William, who had several children, according to your post on the familyhistory.com Seaver board.
I just had the thought that perhaps it was Brookline NH instead of MA.I will go check my database and get back to you soon.No luck, sorry.
I did see the family of William Seaver (age 44) in the 1850 census in Pamelia, Jefferson county, NY, born in MA.This indicates that all of the children were born in NY.
I checked the Brookline MA VR book data for Seaver and don't see births or marriages for a Joseph born 1771 or William born ca 1802.My recollection is that Brookline MA records are incomplete, however.
There was a William Seaver in Rutland VT in 1830 (aged 30-40), so not your guy.I don't see any Seaver or variant in Brookline MA in 1800 through 1840 census.But we all know that the census data is imperfect!
I'll keep working on it.
Do you know where and when Joseph Seaver died?Do you know his wife's name and parentage?