WOW....talk about a lot of names....those alone, who attended the marriage, make my head ache!!!From too little to too much, kiddo...but, I'll see if I can 'plow through' and find something for you.
There is no PA will for Thomas Gregg, at least not in Chester or surrounding counties...this is the only one I found that might he family, so stick it away somewhere in case it might fit later;
Pennsylvania Wills, 1682-1834
GREGG, ISAAC. Kennett.
November 2, 1807: November 16, 1807.Provides for wife, who is not named.To son Samuel the land whereon I now live, formerly belonging to my father, except a strip as described, he paying to his sisters Elizabeth,Mary, Hannah, Sarah and Ruth £100 to be divided; also to have the boy called George Richardson.
To Solomon the tract of land whereon he now lives, called the Fulling Mill place, with the strip reserved in the devise to Samuel; also £50.To son Thomas the land I bought of William Phillips, called the Millhous land. Remainder to 5 daughters above named.Executors: Sons Samuel and Thomas Gregg.Wits.: George Gregg, Joseph Gregg, William Phillips.
(as this Gregg lived inKennett, I looked at theKennett MM records, and there are, literally, pages of Greggs...hundreds of entries...but, no marriage for a Thomas and Rebekah, and nothing for George that would fit your timeline.Nothing for the Sinklars, either...you need to search for several other name spellings that are used interchangeably in Chester Records..Sinkler/Sinclair/St Clair/Sinklar)....
IMMIGRATION OF THE IRISAH QUAKERS INTO PA 1682-1750 says that Thomas Gregg, and other "Irish" Quakers, located near Redstone Fort...and, he was from Kennett...these people were NOT Irish, but English Quakers who had emigrated to Ireland in the hopes of escaping persecution, but when this failed they came to the New World with Wm Penn, to establish a Quaker commonwealth. Wm Gregg arrived in 1685 and had children John, Richard, Ann and George.
I found a few things; Rebekah's maiden name was Janny, and she was the dau of Jacob and Hannah Janny.
from the Goose Creek records....Rebekah (Janny) Gregg, widow of Thomas Gregg and dt Jacob and Hannah, m 2nd time 25-8-1802 at Goose Creek Jacob McKay, s Robert and Patience (Job) McKay, as his 2nd wife.
1812-9-22 Samuel and w Ann and Ch Eli, Gulialma, Phineas, Wm, Isaac, Asa and Tacy, received a certificate to move to the Plainfield MM..before the move, Gulielena was disowned for marrying someone not a Quaker
In the Alum Creek meeting recoreds;
1828-7-21Tacy McVey (form. Gregg)..disowned for marrying a non Quaker
1829-1-29Asa Gregg dis JH (this means that he left the orthodox Quaker meeting and joined the Hicksite form of Quakerism...therefor, he was disowned and will appear on no further Quaker records. - his brothers Eli and Phineas and Isaac did the same
in 1824, brother Wm requested a cert for the Plainfield meeting. I can find nothing about Isaac.