In 1657 George Cubishe purchased 100 acres of land (part of a larger 1500 acre parcel south of the James River originally known as Merchant's Hope, and jointly held by several merchants) from Patrick Jackson & Richard Baker. I had the date when George completed his payments to the prior owners and receive his grant, but can't put my hands on the reference at the moment. Sorry, but maybe you can find it in the Library of VA archives.
In Feb 1664 Robert Abernathy purchased from Patrick Jackson 100 acres of land that had initially been part of that same 1500 acre parcel, and was likely located near the land purchased by George Cubishe. Robert received his grant in March the following year (Patent book 5, p. 567).
In May of 1665, Robert Abernathy and Thos. Parham both sat on a coroners jury. Thomas Parham, George Cubisha, and Robert Abernathy were all clearly neighbors.
Robert's son, we now believe, married Christian Parham, whose mother's 2nd husband was apparently a Tillman, but was probably not the same Susannah Tillman of Billingsgate, London who in 1716 made her son-in-law Robert Abernathy executor of her estate.
Your conjecture that Robert's bondservice was possibly sold to the Tillmans or Parhams or Cubishas is in serious doubt due to an item dated April 21st 1656 in the Charles City County Court Records 1655-1658, LDS call numbers 30989 and 30990. It strongly implys that his services were sold to George Armstrong. Robert's bondservice involved the cultivation of tobacco. See various other dated Court Orders detailing the payment of tobacco during the years he was a bondservant.
Robert probably did participate in occasional fights against the Indians, as did every able-bodied male in the colony. And we are now sure that he was born on or just before 3 April of 1633 somewhere in Scotland. Possibly the lowlands rather than the highlands.
We also know that he married Sara Cubishe in 1657, as soon as he was legally able to do so as a free man. Likely she, too, had been a bondservant, probably sister of George Cubiahe. The child mentioned in "The Cow Document" had probably been fathered by Robert, not by some unknown and supposidly rich 1st husband.
Court orders also give us the fact that in 1661 an orphaned boy, Patrick Ramsey, was bound to Robert Abernathy until age 21. Presumably to be taught to grow tobacco.
In 1662 James Wallace acknowledged he had received full satisfaction from Robert Abernethy regarding the cattle that Robert had in his custody pertaining to the orphaned Patrick Ramsey.