Yes they were Germanic. I stop at saying German as there was no Germany at the time. I would suppose they were from the Palatinate or Alsace regions. Either way, they were Lutheran/Reformed depending on the records you find them in. When my ancestors came to Muskingum Co., OH, they were initial members of the Lutheran church there.
I know about the connection between Frederick Co., MD and Loudoun. My other two Germanic families, the Werts and Hoffs were living in both places. The Hoffs were members of St. Peter's Lutheran in Woodsboro which also had many Adams there.
I've looked at many of the records in both places and still no trace of Wilhelm/William. The only one is the birth record for George W. Adams in New Jerusalem Lutheran in Loudoun that gives his parents names as Wilhelm and Barbara. This is the only mention of them I can find.
Two sisters may have come with him to Muskingum and in their obituaries it is stated their father's name was William and that the older sister, married at the time of her parents death in Loudoun, took in her sister and brought her to Muskingum with her and her husband. An article on George's son William Washington Adams, gives his grandfather's name also as William. There are a few William Adams in Loudoun, one married to someone other than Barbara so without some other documents, I can't say who is who. Nobody knows where they are buried either.
The document you quoted is interesting. It is similar to the oaths of allegiance made by many Pennsylvania immigrants. While the oaths were made to the colonies, this would be pledging allegiance to the King. Since Maryland was owned by the King and governed by his cronies, this is not surprising.
Most of my research on all of these families is concentrated in both Loudoun Co., VA and Frederick Co., MD. I don't think any serious researcher can ignore families being in both areas. Even my ancestor Philip Hoff's probate record cites land still owned by him in Frederick and also that a debt to a doctor there should be paid in Maryland currency.
One can also not ignore the migration route south into Frederickand Loudoun from York, Lancaster and Berks counties in PA. I know many families had members from those areas move south into both areas and also further south into the Shenendoah valley. It helped that Frederick and Loudoun were right in the middle of the crossroads of those migration paths and also on the banks of the Potomoc.
I cant tell what "Haritas Fiahum" is supposed to be. It looks like Latin but I can't find anuything on it. The only hits on "Haritas" comes from the Turkish language.
"Sociates of the Papisty" may be "Sociates of the Papistry". The dictionary refers to papistry as a noun "Usually Disparaging the Roman Catholic Church." This would be a good description of what the Lutherans and Reformers were. "Sociates" was usually a shortened form of Associates and in this case probably meant a member of a religious group that did not agree with the Roman Catholic Church. Surely they would be welcomed friends of the Anglican church who had their own bad history with the Catholics.