Hello Steve, don't get me wrong.... I am talking about descent over millennia here... I am an anthropologist and have spent a lot of my time researching descent from Antiquity and long term migration patterns...
Thomas Mustain clearly had his origins in the British Isles in terms of immediate lineage. I believe he belonged to the family of Taine's recorded in Bermuda, Barbados, and Jamaica. Both Thomas and Jesse were Anglicans not Jewish neither were they Morisco or Melungeon. Marriage records show Anglican, Quaker, and Huguenot affiliation for the Taine, Moustin, M'Taine, and Muston families that emigrated to Americas in the 1500-1700 time frame.
These migration patterns of these surnames from 1000 AD - 1750 are as follows (I am creating a map to show the relationships). Brittany to England - (within England to Wales, Brittany, Cornwall, Channel Islands). With the advent of persecution in France they migrated to Holland, Canada, Ireland and the Caribbean. From Holland they migrated to Scandinavia, Germany, New Amsterdam, Canada and the Caribbean. From Ireland they migrated to Canada, North America and the Caribbean.
The Moorish/Arab name Al Musta'in is not the same as Mustain although there is some similarity in the creed of Mostyn (Auxillum meum et Dominum) and the Arab meaning of the name Al Musta'in (one who prays to God for intercession). I am not entirely discounting a connection however..more research will need to be done before we can say yay or nay with any certainty.
In fact the centuries old Anglophilic definition of the origin of the surname Mostyn (Moss town) is under scrutiny. The name does have an alternative Latin meaning "tin mine". Incidentally the same root behind Brittanium. My research so far shows that in England most of the town names derived from Mostin are in some way associated with mining (tin, silver, or coal) or with families with mining interests. This was certainly true of Isaac of Muston. If the name Mustain is in any way connected to Musta'in it would have had to be prior to 500AD.
I highly suspect that any Arabic genes infused into the lineage may have come from secondary sources not from the main Mustaine ancestral line but from an Admixture introduced between 1000AD and 1700AD through a Portuguese or Spanish intermarriage. Regarding the name Seludy there were a great many girls of from this area in 1700-1780 who were named Seluda, Seludi, Seludie after then Seluda river in Carolina. http://en.wikipedia.org/wiki/Saluda_Riverhttp://en.wikipedia.org/wiki/Saluda_River
With regard to that... this bolsters my believe that the next step to locating our Thomas Mustain is to look in the islands of the Caribbean where there was two generations of Jesse Taine living in Barbados. One Jesse Taine married a Joan Browne in the Anglican Parish in 1725. At the baptism of their son William some years later there was a Jesse Tain who was made Godfather of little William. I found a record of a Jesse Tayn who emigrated from the Caribbean to South Carolina prior to 1740 accompanied by a William Browne. It would appear also that our verifiable Thomas Mustain was not the original Thomas (first ancestor) but rather his son.
Land records indicate that Thomas Mustain recieved a land grant in 1722. Since he would have had to be an adult to recieve the grant. This Thomas would have had to be our Thomas's father. If our Thomas had been an adult in 1722 he would have been too old to be the Thomas Mustain that partipated in the American Revolution.
Here is what I know so far...
There is a record of Marc Taine aka Marc Moustin serving as an alderman in Calais. He is also associated with the Enterprise of America (French West India Company) which in 1560 sent settlers to Martinique to raise sugar cane and tobacco. One of these settlers was a Marie Taine (possibly Marc's sister). There is also at this time a Antoine Taine/Mustin also from Calais who was instrumental the settlement of New Amsterdam and Canada.
There is a record of a Thomas and Ann Moustine who debarked in MD 1670, in 1701 there is a record of a Thomas Taine baptized son of Thomas Taine and Jeanne Cornu in Calais France. There is also a John Mustain recorded in MD around 1660. (Maryland is very close to Halifax/ Pittsylvania county VA.)
There is a Jesse Taine in Barbados married Joan Browne in 1725 and emigrated to South Carolina in abt 1740. There is a second Jesse Taine who is obviously related to the first Jesse Taine (whether senior or junior I am not yet certain).
One thing I am sure of the (M'Taine/Mustain) family did not come to the Carribean as indentured servants, nor did they come by way of Bristol, Middlesex, or London. They would likely have sailed from the ports of France, Holland, or Ireland. Most likely as the owners of their own ships, or as fully paid passengers.
BTW... There is some indication that our Thomas may have been a (clerk, lawyer, or legal notary).
One additional aside not sure how it is related... There is a record of a Thomas Mostyn and Browne (T/P)ayne located at Puddledock up Thames London in 1730 as the insurance underwriters for port shipments of sugar between the colonies and Dutch and English ports. The name of the insurance company at the time was the Sun Assurance Company. in 1781 ownership was transferred and the name changed to Phoenix Assurance.