The 1850 Hillsdale census is the one that shows Stephen H. has children of the Roberts family under his roof while at the same time he has placed his own children Sarah & Hiram in the home of another family. (The Purchases.)
The Hillsdale ledger entry regarding Hannah Hungerford's death lists her parents as Mr & Mrs Joseph Maxon.
At the moment I can see just one plausible way in which these things can be resolved. It goes like this:
Hannah (Beebe) Hungerford died in the 1840s.Stephen remarried to Hannah (Maxon) Roberts -- who later died as a Hannah Hungerford. There were two Roberts males listed in the 1850 Hillsdale census. There was just one in 1860, but I've not yet had a chance to dig further.
When Stephen married second wife Hannah he also had to take on the burden of caring for her fatherless children. This would explain the Roberts surname of the kids. But, unable to feed all the mouths, he placed his children in the home of the Purchases, long trusted & associated with the Hungerfords.