Yes, Jean I have researched your McClary family and they have been tough. In the 1820 census for Orange County, VARobert McClaray of Orange County, VA has a son the right age to be Tandy but not William. The census had Robert with one son age 10 to 16 (Tandy)and one son 16 to 18 (?). I cannot find William in 1820 under any possible spelling. In the 1840 census for Orange County, VA, William is listed in the 40 to 50 age group (born between 1790 and 1800)and Tandy in the 30 to 40 age group (1800 to 1810). My guess is William should have been entered in the 16 to 26 age group in the 1820 census.
I do believe Robert McClary is the father of William and Tandy. Robert is in the right age group to be the son of Hugh McClary of Augusta County, VA. Robert gives his age as over 45 in the 1820 census which means he would have been born circa 1775 or before. The problem I have with this scenario is the naming patterns but they don't always hold true.
The name Tandy is a Scot pet name for Andrew and was widely used in that time period. In 1820 census for Virginia there were 10 individuals listed with the given name Tandy and two families with the surname Tandy.
I wish I could be more help Jean. There are three families I would pursue. The Andrew McClary (McCleary) family from York County, PA; the William McClary family of York County, VA and Robert McClary the son of Hugh McClary of Augusta County, VA.
Good luck in your research efforts. If I run across anything I will let you know. Glain