With regard to the Stephen of Keeler, Van Buren Co.You said you believed this was the one married to Hannah Beebe.The census data you sent shows a 20-30 year old male & female, - which I presume are the parents in the family.If not, then the wife was productive for almost 25 years. Given the birth years now known for this couple, Stephen would have been 46 in 1840 and Hannah would have been 40.
The 1840 census shows 2 males under five years. But there was James, age 15, and Hiram, age 2. (Hiram is the one whose death ledger entry names Hannah (Annie) & Stephen as his parents.)The census says there was one female under 5 years. But Sarah was then 8 years old. I've had the impression that the 1840 census named only heads of house.
Given the fact that three parcels of farmland in Hillsdale were sold to Elias, Edwin & James Hungerford, we can presume a close relationship existed between the three young men, even if they did not share the same parents. A rather recent finding was that Elias was the son of Nathaniel, Jr. There is a possibility that Stephen, Hannah's spouse, was a brother of Nathaniel, Jr.The time period is right and Connecticut is the right state.You mentioned that Nathaniel had a son named Steven (wife Eliza Paddock). That name may have been given with his (Nathaniel's)brother in mind.