With so many people with the exact same names it is hard to sort them out. The early John and Tobias are no doubt two of the five sons of Peter Stalcop who all moved into Orange Co. NC. This list shows that Tobias lived in Northern VA for at least two years before going into NC.
The later William from the 1782-1810 Loudoun Co. Personal Property Tax List is probably the son of Matthias Stalcop. This William moved to Ohio.
If Tobias was married in a church wedding there is likely no record of it today unless somehow the church records were (1) even made, and (2) they have survived. I read somewhere (State Lib?) that less than half of all VA marriages are on record.
Earl Johns gave a brief summary of what happened to each of the children he listed for Tobias.