The "original" Peter, according to Angstadt family info as I've seen it, was a brother to Adam and was a son of the original immigrant Hans George Angstadt. There is no evidence at all that this Peter (Peter 1) was a gunsmith, only some anecdote with no source info to back this up. Peter 2 was a son of Adam and it seems fairly clear that he made most if not all of the Peter Angstadt signed or attributed rifles, beginning (probably earliest) with the lion-carved pieces ca. late 1780s or more likely through the 1790s. He was born 1763 so I sincerely doubt he was involved in gun work until after the War was over. There there seems to have been a 3rd Peter as you note, although I have not been able to definitively place him. I don't think he was a son of Peter 2, in fact I'm not clear on any children of Peter 2. His will of 1815 and probate mentions only his wife Catherine who was left with fairly substantial debt.
Many of the old county histories and family anecdote mention Hans George Angstadt as a gunsmith on the 'Lobachsville Pike' or Lobachsville road, but I think these anecdotes are actually misplaced remembrance of Johannes Moll who was on 50 acres fairly adjoining the Angstadt farm and was actually documented as a gunsmith there in Rockland twp by 1752/1753, before moving to Allentown in the early 1760s. There is absolutely no evidence that Hans George Angstadt was a gunsmith or gun stocker. Moll could not have trained Peter 2 unless he (Peter) moved to Allentown as a child, as Moll was already in Allentown by the time Peter 2 was born.
The rifles that Kindig attributed as 'early Molls' are very interesting pieces, and there are at least 3 or 4 more of them by the same guy in addition to those pictured in Kindig. One of them was pictured and discussed here long ago as being found in a wall down in NC, with a patchbox that resembles a hand holding a violin neck, but the whole story fell apart when seriously examined and furthermore, someone soon after butchered the gun in an attempt to spuriously alter it so as to try to tie it to Moravian work. Much discussion was made of Jacob Loesch but it seems quite unlikely. I don't know who the guy was who was stocking up those rifles in question, but there are some small similarities with some of the Angstadt work. They do seem to have originated somewhere in Northampton or eastern Berks Co, but none of them are signed. They also appear to be earlier than the Peter (2) Angstadt rifles we are discussing. The gentleman you mention has one also, very interesting piece with what appears to be stamped box engraving. To my knowledge none of this string of rifles are signed but they all are clearly made by one man or one shop. Big mystery!