These are some fascinating references and intriguing developments. I've checked the Doris Dockstader-Rooney source for Hendrick (b. 1741) again, and there does not seem to be any material evidence linking him to Hendrick Jury (b. 1714), not even family history – so if indeed there is a microfilm reference to Henry Dockstader of Caistor Township that says he is a son of "John Dockstader", that would settle the issue of parentage (at least as far as first names go):
George Dachstaetter (b. between June 12, 1778 and June 11, 1779 in Germany)
m. Anna Elizabeth UNKNOWN
John ____ Dachsteder (b. 1715? 1720? in New York State)
Hendrick Dachsteder (b. estimated about 1741 but uncertain, age not stated in will)
m. Maria Magdalena WEBER (b. ? )
John Dachsteder (b. between December 2, 1750 and December 1, 1751)
m. i) a Cayuga woman ( b. ? )
m. ii) an Onondaga woman (b. ? )
Frederick Dachsteder (b. ?)
m. Elizabeth STEVENS (b. December 1764)
Given the ages of all involved, I would again think that the last three must have been grandsons of the original settler. If not sons of Hendrick (b. 1714), it's possible they may have been the sons of Johann Leonard Dockstader (birth placed in 1720 by Doris Dockstader Rooney); this son of Georg is known only from the Lutheran church registry of 1743, where he is listed as Jurgen's son (Jurg and Jurgen being alternative renderings of the name Georg). Or perhaps "John Sr" is another son of Georg that is not yet attested. If John Sr is indeed a tenth son of Anna and Georg, as Barker has it, that's quite a few children!
However, another possibility I was going to mention earlier involves the so-called four sons of the first marriage of Georg Adam (b. 1709) – these are Hendrick Jury (a different Hendrick Jury, born about 1721 – family history), Peter (b. about 1723 – gravestone), Abram (b. between 1726 and 1733 – family history), and Johann Georg (1728-1808 – gravestone). These four Dockstaders have been taken to be the sons of Georg's oldest son George Adam (b. 1709) and an unknown first wife, prior to George Adam's marrying Anna Catherine Stahring (b. 1714) and their having a first child, George Adam Jr. (b. 1736). However, this assumes that George Adam was married and had children by age 12 – and a "first wife" is posited because Anna Catherine would have been 7! How this hypothesis developed I can't fathom, but Doris Dockstader-Rooney questions its validity in Volume 1 and I have seen remarks on its mass improbability elsewhere as well.
These four sons have probably been attributed to George Adam (b. 1709) on the basis that he is the oldest son of Georg, and therefore the most likely (even if 12 years old at the time) candidate to be their father. However, I would posit that these four Dockstaders are more probably the sons of the *original* settler, Georg Dachstaetter, since in my mind he is the only Dockstader old enough to be their father. In this connection I have long since ruled out the "other Dockstader immigrant" possibility – Georg and his wife and infant son (b. 1709) were absolutely the only Dockstader immigrants to New York. It is also possible that Georg's name (which we know to have been more fully "Johann Georg Dachstaetter" from his trip out of Germany) was actually "Johann Georg Adam Dachstaetter". In any case, anything seems more probable than a 12-year-old and a 7-year old having children.
If we were to accept this last scenario, it would take Georg Dachstaetter's known offspring count all the way up to 11 sons and 1 daughter. If one can hardly believe his wife Anna Elizabeth to have endured all this, it is also possible that she died at some point and was not actually the mother of Georg's later children – Anna Elizabeth is not listed in the church registry of 1743 (the same one in which Johann Leonard appears next to 'Jurgen'), and may already have been deceased for quite some time. However, no other wife is registered next to Georg in her place.
As for Native ties, my belief is that Captain John's ties to the Iroquois transcends just his marriage and probably applies to his family as well since two of his brothers also joined the Indian Department. If this was the first response of three loyalist brothers, on three independent occasions between 1776 and about 1779, my instinct tells me that either their father had been involved in the French and Indian wars extensively, or the brothers were part native themselves, or both. John is more or less known to have had a native wife prior to his move to the Grand River, and perhaps it can be argued that this explains his joining the Indian Department. However: even if John's first marriage took place before the winter at Cayuga in November 1777, it would not explain the reaction of his brothers. Frederick, who was unmarried, joined the Indian Department a full year before John did, and later so did brother Henry – and Henry's wife (Magdalena) was not native. In any case, even if the Indian Department did draft non-native white men with extensive knowledge of native life and warfare, it would have been a decidedly odd UE regiment for three white brothers to wind up in – especially since *Butler's Rangers* was the unit specifically designed for white loyalists with knowledge of native warfare, to accompany the Indian Department. Frederick transferred over to the Rangers in 1777, but John and Hendrick remained in the Indian Department for the full length of the war as far as I know.
One more possibility to consider is that if our hypothetical John Dockstader Sr was born between 1715 and 1720 (or perhaps even later, as a fifth son of Georg's last four sons), there's a fair chance he was still alive at the time of the Revolution and later came to Canada with one of his sons, much as George Adam Sr. appears to have done in Montreal.
(Note that all of the above points are, of course, conjecture!)
One last unrelated correction is the date of Lieutenant / Captain John Dockstader's death. The full obituary column of the Niagara Herald, February 28, 1801, reads:
DIED. – At Grand River, on Monday last, Capt. JOHN DACHSTEDER. – At York, lately, Mr McBride.
February 28, 1801 was a Saturday – so presumably John Dachsteder died on Monday, February 23, 1801. So now at least one date in all this business has been confirmed.