It would be helpful if you would give some kind of vital or keystone dates for the two Henrys you ask about.

One Henry Snider died in or about 1805, when is estate inventory was taken. I think this is the Henry Snider associated with the James Stanley family, and I think also came from Frederick Co. MD.

You would probably have the best luck with going directly to the records, examining the Land Book tax assessments and land records. With any luck there would be an estate settlement for the one who died ca. 1805, listing heirs, and/or County Court records appointing a guardian for any minor children.

With luck there could be heirs' deeds concerning disposition of the respective lands of at least one of the Henrys, that would identify the heirs by where they resided.

Bear in mind that publishers of County Histories by and large do not do genealogical research, so should most often be disregarded. This goes for the author of the multi-volume History of Monongalia Co. too.

There is no substitute for the satisfaction of careful work in available actual records.

Good hunting,
Jade