After checking around some more, it appears that the the older John Dickert of Milford Twp. and his wife were probably born no later than the 1750's and were therefore too old to be the parents of the John who was born c. 1799.

A more likely candidate might be Peter Dickert/Dickart/Deckert, who appears on the 1810 and 1820 censuses in Nockamixon Twp. and the 1830 census in Milford Twp. Putting those censuses together, it appears that Peter was born in the early 1760's and his wife probably in the early 1770's. They seem to have had 5 sons and 3 daughters, with the oldest son born in 1795/1800 and the two youngest in 1811/15.

That would mean they could have easily been the parents of both John and Jacob -- as well as of Joseph Dickert of Springfield Twp., who was born c. 1812.

Given that Peter wound up in Milford Twp., I would guess he was a close relative of the oldest John Dickert -- most likely a younger brother. But, of course, all of this is highly speculative unless wills or church records can be found to back it up.