You say that you think Isaac Henley Hagler of Bibb County was related to Peter and John Hagler of Autanga County, AL. What you failed to mention is the location of Bibb County and the time period.
The Peter Hagler that I am familiar with was the son of John who was a cripple who died in 1811 and this John was the son of John the immigrant Hagler who died before May 1772 and both of these John`s lived in that part of Mecklenburg County, NC that in 1792 became Cabarrus County.
Peter was married multiple times and his third wife was Margaret Polk d/o John and Elizabeth and Margaret was a cousin of U.S. President James K. Polk. In December 1835 Peter sold his 715 acre plantation in what was Anson that in 1842 became Union County, NC and his mill on Rocky River. Then withthe children by his previous marriages "set sail" for Dale County, Alabama abandoning his wife and their three infant children in North Carolina.
Shortly after arriving in Alabama Peter acquired a "paramour" in the person of Sarah "Sally" Cooley.