Family is speculative. See notes for William b.1750. David and William associate together in Franklin Co, VA. Most likely connected with Thomas' of Amelia Co, VA who came from Gloucester Co, VA.
Alternate theory is they came from York Co, PA with the Diehl/Teel's . I have found DNA matches to Teel descendants which suggest William was -in-law to the Diehl's! Indeed, the Diehl's came from an area in York Co, PA next to Thomasville (Dover is 6 miles away). Curiously, Ephraim Thomas formed Thomasville in Oregon Co, MO when he moved there. Which leads to this record:
"All Private Church Registers to 1800, York County, Pennsylvania" on ancestry.com:
Name: Dorothea Thomas
Description: Bride
Event: Marriage
Date of Event: May 1770
Place: York Co., PA
Remarks: From Hanover and Lebanon
Church: Records of Baptisms and Marriages by Rev. Johan Stoever for York County, Pennsylvania, 1730-1779
===> groom appears to be "Peter Thomas" and bride is named "Dorothea Strohfuss" May 20, 1770, 11 months before Ephraim Thomas was born.
https://archive.org/stream/recordsofrevjohn01stoe/recordsofrevjohn01stoe_djvu.txt
==> might be a brother of William & David.
If you found a relative, please sign my