Individual Details

Isaac has proved to be elusive. There was apparently some kind of estate settlement in 1801 when Israel Harmon testified to the children of Jennie - Stephen, Samuel & Sarah. It could have been Israel's or even that of a wife if Isaac Gibson left a will that's not been found.

There were Gibsons noted in tax records in Lincoln Co KY, but only for the one year.
1793 - A John Gibson, 1 tithe, 5 horses, 6 cows and a Samuel Gibson, 1 tithe, 1 horse, 2 cows

Richard Davis sent:
An Isaac Gibson lived at Bourbon County, Kentucky;
Court records Book A 1786-1793.
On 16 Jun 1790 Isaac Gibson was paid 600 pounds of tobacco for 6 old wolf heads.
Sep 1790 James Dozer sued Samuel Gibson.
May 1791 Samuel Johnston sued Samuel Gibson

There were other mentions for Samuel Gibson in court records after 1791, but none for Isaac Gibson. It is possible Samuel was a brother to Jennie.

Samuel Gibson. He married Mary. In 1802 at Bourbon County, Kentucky. “I Samuel Gibson as guardian to the within named Rachel Gibson do give my consent to issuing the license within mentioned. Given under hand and seal the date within mentioned” and he signed his name. On 29 Mar a bond by John Maxwell and Samuel Gibson bound to James Garrard Governor of Kentucky for marriage of John Maxwell and Rachel Gibson. At Bourbon County “This is to certify that I Mary Gipson do give consent for John Maxwell to be joined to my daughter Rachel in the bonds of matrimony given under my hand this 29 March 1802”.
1. [?] Samuel Gibson, b. c1770. He married Elizabeth Baird on 12 Apr 1791 at Bourbon County, Kentucky with bondsman Elizabeth Baird. The bond was dated 11 Apr 1791. He may be the Samuel Gibson who had a marriage bond with Isabella Rogers on 25 Jul 1796 with bondsman Benjamin Rogers. The marriage is not found in the marriage register. In Jun 1793, John Dannelson married Elizabeth McCoy at Bourbon County with consent by Samuel Gibson Jr which was given 15 Jun 1793 by Bond.
2. Rachel Gibson, b. c1783. She married John Maxwell in March 1802 at Bourbon County, Kentucky.

Tax records Bourbon County, Kentucky
1787 Isaac Gibson 1 over 21, 1 age 16-21 no slaves 1 horse and 4 cattle.
1788 Isaac Gibson 1 over 21, 1 horse
1789 Isaac Gibson 1 over 21, 1 horse
1790 Isaac Gibson 1 over 12, 3 horses
1791 Isaac Gibson 1 over 21, 3 horses

1792
29 Sep Samuel Gibson, none over 21, 1 age 16-21 no slaves, 4 horses and 15 cattle
4 Jan William Gibson 1 over 21 no slaves or horses or cattle

1793
19 Oct Samuel Gibson, none over 21, 1 age 16-21, 5 horses, 17 cattle
8 Nov Samuel Gibson 1 over 21, 3 slaves, 6 horses and 12 cattle

1795 John Gibson land in Clarke County, 2 over 21, no horses or slaves
1796 Samuel Gibson 1 over 21, no slaves, 5 horses and 18 cattle
1797
Samuel Gibson 1 over 21, 2 slaves, 3 horses, 61 acres
Another list Samuel Gibson 1 over 21, 6 horses and no land
1798 missng
1799 Samuel Gibson 1 over 21, 1 slave, 3 horses
1800
Samuel Gibson Sr. 51 acres on waters of Hinkston, Bourbon County in Harri’s name surveyed by Daniel Boon, 1 over 21, 2 slaves and 3 horses

1802
Samuel Gibson 61 acres in Hinkston 1 over 21 and 2 horses
Away Samuel Gibson 58 ¾ acres on waters of Stoner 1 over 21, 3 horses

1803
Samuel Gibson 61 acres on Hinkston 1 over 21, 1 slave, 2 horses
Next to Samuel Gibson Jr. 58 ¼ acres on Stoner 1 over 21 and 3 horses

1804 Samuel Gibson 58 acres on Stoner 1 over 21 and 3 horses
Next to Samuel Gibson 61 acres on Hinkston 1 over 21 , 1 slave and 2 horses
[Stopped here.]

I looked at this awhile ago, so I don't remember looking at all of the court records or deed records. I find it interesting because there is an Isaac and a Samuel Gibson.
Israel Harman named his second son Samuel, and this was not a name found in the Harmon family.

The Samuel Gibson named here later filed for his Rev War pension from Highland Co, Ohio where he stated he had moved in 1804 - when his wife Elizabeth applied for her widow's pension she had to get a copy of the above marriage record. He had served for over two years, fought at King's Mountain. Samuel died 19 Feb 1835 in Highland Co, Ohio.
Samuel served from Washington Co VA and that's where he returned from service circa 1782. From the tax list for Washington Co, 1782:
Capt. Barnet’s precinct
James Gibson over 21, 6 horses 9 cattle
Capt John Kinkeads precinct
John Gibson none over 21, 1 horse and 3 cattle
Col. Aron Lewis precinct
Samuel Gibson 1 over 21, 6 horses 11 cattle
12 away
James Gibson none over 21, 5 horses and 15 cattle
Far away on same list
Samuel Gibson 1 over 21, 6 horses and 9 cattle and 2 slaves
http://www.newrivernotes.com/va/wash1782.htm

Child

Jane "Jenny" Gibson ( - 1787)