From Rob - Names to keep in mind while doing our research:

James Reddish- Alexander is a witness to his son's will

Robert Crawford- associate of John Scott

John Waugh- Anglican minister from Tyrone Ireland- spent time in Scotland before immigrating

Matthew Steele- merchant in Virginia, Maryland, Barbadoes- mentioned in will of Samuel Sinckler- 1677

John Wilson- Steele's partner in Maryland and Barbadoes- mentions Sinclairs in his apparent Barbados will

Thomas Monteith of Glasgow- Thomas Sinclair indentures to pay a debt to him in Stafford County, Virginia

John Douglas- son of Douglas of Mains- emigrates to Virginia in 1655- Isaac marries his descendant, Letitia. (later - The (Douglas of) Mains in question was southeast of Glasgow. I believe, in Lanarkshire.)

William Stone- listed as a tither in Alexander's household 1724

James Ewell- a neighbor and friend of Alexander

Robert Kingsbury- business partner of John Sinclair of Maryland- 1650s

Ninian Beall- one of the indentures who John Sinclair claims headrights for

Ship Mary of Waterford- a John Sinclair pays her bond in Maryland- 1683

Bogle and Co. vs Sinclair's heirs, 3 Feb, 1767- Special Imparlance- Loudoun County

Updated by Rob -

Boyd family - I know that they were among the ayrshire families to colonize Ireland.

Waugh - also a pronounciation of Veatch and I know that there is an ayrshire family by that name that was active in Virginia and connected with some rleated families.