Sorry, I misread your post. The entries in my database concerning Joseph and Sarah's children were made many years ago before I began documenting everything. My information on Packards outside of my purview of Plymouth County tends to be somewhat sketchy in any case. These entries are incomplete and probably came from an article in Packard's Progress, but as those issues are not indexed and not in PERSI I will have to go through the issues looking for it, and that will take some time. There is an off chance that the information came from one of the town histories, but I'll try Packard's Progress first.
Have you looked in the Corbin Collection? If not, I now have it on CD and can have a look.
I would imagine that you've already checked with the courthouse in Northampton, looking for Joseph's will - that would seem the place to look given his original place of burial. The probate index that I have for that county ends before 1800 and so is of no use. I would also imagine that you've read some of the books on the Lost Towns to see if there is any mention of Joseph's family there - the only one that I have here is of no help.