In answer to the first question: The evidence to support Tabitha as a daughter of Gilbert Platt.
The first piece of evidence I've located comes from James Branch Cabell's "Branchiana" and is as follows:
Thomas Osborne of "Coxendale," born 1641....A legitimate son, oneThomas or EdWard Osborne, and born before 1620....
The will of Captain Thomas Osborne of "Coxendale"....is not recorded at Henrico Court-House.
....the fact is pretty clearly established that Captain Thomas Osborne of "Coxendale" died before 1678 ; and, as has been previously shown, later than the November of 1667. He had issue, so far as known, only one child, a son, whom he survived.
(Edward) Osborne of Henrico.
This only son of Captain Thomas Osborne of "Coxendale" was, perhaps, the Thomas Osborne of "Pasbeheighes," referred to in the " Muster of the Inhabitants of Pasbehays, belonging to the corporation of James City, and in the maine," taken
30th January, 1624-5.
"Thomas Osborn, aged 18 (came to Virginia), in the Francis Bonaventure."
Eighty of these "Governor's men" were sent to Virginia in 1620, the Bonaventure transporting some of them, and it is possible that Thomas Osborne of "Coxendale" embraced this opportunity of securing free transportation for his heir, and that his son and this Thomas Osborne " of Pasbehaighes" were one and the same person.
....the probabilities are rather in favor of this son of Captain Thomas Osborne having been the Edward Osborne of Henrico who patented (2nd June, 1636) some 400 acres of land in Henrico County—"adjoining a swamp called the great swamp, and the river"— fifty acres of the same being due for his personal adventure, and 350 acres for the transportation of seven persons. the probabilities are rather in favor of this son of Captain Thomas Osborne having been the Edward Osborne of Henrico who patented (2nd June, 1636) some 400 acres of land in Henrico County—"adjoining a swamp called the great swamp, and the river"— fifty acres of the same being due for his personal adventure, and 350 acres for the transportation of seven persons.
The son of Captain Thomas [Edward] Osborne of "Coxendale," whatever may have been his Christian name, died in Virginia about the year 1650—certainly not earlier than 1646—having had issue:
I. Thomas Osborne of "Coxendale," born 1641, with whom we shall hereafter have to do.
II. Edward Osborne of Henrico.
Edward Osborne of Henrico, the younger son of the foregoing, was born in 1646.
At the death of Captain Thomas Osborne of "Coxendale," his estate was divided between his two grandsons— both of whom had survived their father—in what proportion it is impossible to say, although it is apparent that to Edward Osborne's share fell the northern part of the plantation.
He appears to have farmed it prosperously, and to have increased its dimensions ; and the last act recorded of Edward Osborne is that within the last year of his life, on 1st of June, 1696, he purchased some 200 acres of the southern portion of "Coxendale," which his elder brother, now dead, had inherited, and had long ago deeded to his own eldest son.
It is not recorded that Edward Osborne of Henrico ever held any political office or took any part in public life.
He died about the beginning of the year 1697, and it is to be regretted that the ambiguous wording of his will prevents estimation of what lands he then possessed, since he was undoubtedly well-to-do in the world.
Edward Osborne of Henrico married, prior to 1676, "Tabitha Platt, the daughter of Gilbert Platt of Fauldinge," in Virginia, whom he survived.
By Tabitha Platt, Edward Osborne of Henrico had issue :
I. Tabitha Osborne, who, as previously recorded, married Benjamin Branch of Henrico.
II. Edward Osborne of Henrico, born post 1677, and died in 1732, leaving issue.
III. Martha Osborne.
The will of Edward Osborne of Henrico County, in the Parish of Varina, is recorded at Henrico Court-House.
It is dated 6th of January, 1696, and was recorded 1st of April, 1697.
"To the testator's son, Edward Osborne, is bequeathed "all my lands in generall,....One negro woman named Moll, with her increase (excepting the first child she bringeth, which I give to my daughter, Martha Osborne)....To the testator's daughter, Martha Osborne, is be- queathed in similar fashion."
The testator's daughter, Tabitha Osborne Branch, now married to Benjamin Branch of Henrico, is not mentioned in the will, and it is deducible that the testator had previously provided for her; but the testator appoints his son-in-law, Benjamin Branch, to be his executor....
The witnesses of this will are Samuel Branch (the brother of Benjamin Branch of Henrico), and Martha Osborne (the widow of the testator's older brother), and Joseph Tanner (the half-brother of the testator's wife).
About 1675, Edward Osborne of Henrico married, as previously recorded, Tabitha Platt, the daughter of Gilbert Platt of "Fauldinge." Tabitha Platt Osborne was born about 1660, and died between the years 1692 and 1695, being survived by her husband. To him, as recorded, she had borne two daughters and a son.