Thanks for taking the time to post your findings -- You have quite clearly have given a lot of thought to your posting! A couple of additional items to consider:
1. John Province received 160 acres in Madison County, Alabama (Military Warrant 1057) on Jan 7, 1811 next to Ebenezer Byrum who received his land 27 Nov 1812 [Military Warrant 1147]. I suspect that the warrant for John was for his service as a Washington County, Pennsylvania Frontier Ranger ~ 1782. Thomas Province similarly served in the First Battalion, Washington County, Pennsylvania circa 1782 – 1785 although I did not find a military warrant for Thomas.
2. From Washington County, Pa to East Tennessee to Alabama John, Thomas Jr., and Thomas Sr. are relatively visible in the historical records. What is troubling is that William is almost invisible from 1799 (Hawkins County records) to 1830 Jackson County, Alabama.
Even then his records are relatively limited to the 1830 and 1840 census with almost no activity as a witness to deeds, wills, court appearances, etc.~~~ The smoking gun that you mentioned would take a great step forward if someone/anyone could definitely locate William from 1799 to 1830, i.e., I’m strongly leaning toward voting with you on the children but am holding an open mind until I can nail down William :-)
3. As for which siblings are siblings… The 1830 Franklin County, Illinois census not only includes Thomas (p 98) and John Provence (p 112) but also William Millakin (p 100). William and Anne Provence Millican’s son, George Thomas Millican, was born in Illinois on March 28, 1830.
To wit: William Millakin 1 male < 5 (George Tom); 1 male 5 – 10(John P.);1 male 30 – 40 (William)
I would be very surprised if Anne, Thomas, and John were not siblings. Throw in their ties to the Byrams, Maxwells, etc. along with the Bernard’s that you mentioned the evidence does point toward John Province as their father vs. William and Rachel.
4. Note:Thomas Province, Sr. of Washington County, Pa is also thought /conjectured to be a son of Thomas Province born of Frederick County, VA.The rootsweb entry for ‘Cosby/Chimento & Associated Families’ discusses how “Thomas, not mentioned in the will, eventually involved all of the daughters in a lawsuit over the estate, real and personal “. Haven’t verified the information but it is interesting.
Note: If anyone is willing to share court records, etc. for William Province from 1799 to 1830... I would be grateful. I do have some of the records for the William who is a brother of Rev. John Provine Presbyterian minister in East Tn... just not for the other William!