To investigate:

Maybe only Nathaniel & Robert were David’s sons, and Samuel was David’s brother????

Will names Robert & Nathaniel, doesn’t mention Samuel.

See the map with Samuel Steele. It seems clear that in 1747 David Steele was the primary presence in the area shown on the map as belonging to Nathaniel and Robert Steele. Just look at the neighbors in each reference below. Also curious that David’s will mentions Nathaniel and Robert, but not Samuel. Guess is that Samuel was already taken care of, or that maybe Samuel was not David’s son? Could be a brother?

Chalkley Vol 3:
Page 383.--17th October, 1747. Wm. Beverley to Samuel Steel, £17.14.0;
690 acres in Beverley Manor; corner to James Huston; David Steel's land;
corner to Robert Alexander; corner to Patrick Hayes. Teste: Robert
Alexander, Robert Ramsey, John Fulton. Proved by two Roberts, 18th
November, 1747. Proved by John, 22d August, 1766.

Page 432.--19th November, 1747. £27 current money Virginia. George
Brackenridge to Thomas Beard, 309-1/2 acres in Beverley Manor; corner to
James Lynn and John Tate; corner to David Steel. Teste: James Fulton,
Samuel Wilson, Samuel Steel. Acknowledged by George, 18th November,
1747, and Ann releases dower.

Page 24.--Wm. Beverley to Nathaniel Steel, Beverley Manor; corner
John Teat and Geo. Brackenridge, Jno. Lockhart and Ramsey, David Steel,
James Fulton, 17th June, 1748.

Page 217.--5th April, 1749. Wm. Beverley to John Teat, 344 acres in
Beverley Manor. Corner James Linn, Steel's land. Corner Jno. Lockhart,
Brackenridge s line.