Just a theory but a lot of facts fit. The the ship Aurora from Rotterdam arrived in Phila 1744 with Jost (Could be error becaused he signed with a X)and Johann Frevel 3mos old on sailing, with family. Also on the ship was Johann Hermanus Frevel. They came from Hessen-Nassau area of Germany which was also strongly Luthern andhad a strong and growing Moravian church population. Some of the earliest church records (marraiages of Rosina, Rachell and Elizabeth Frevel- supposed daughters of Moses - were in a Moravian Church. Other birth records are also in Moravian church records.
It was common practice for Germans in that area particularly to give children first names of saints eg: Johann = St. John. so it is common for many people to have the same first name. On the ship manifest of the Aurora most men have the name Johann, or variations there to. It is very probable that Issac changed their first names after arriving in Philadelphia.
As noted Johann William was 5mos old and this does not jive with current thought about moses. My thought is that some of the children believed to be his could actually be Issac's children. But if Moses was about one year old on arrival in 1744, he would have been 15 when the oldest girl was born so it is not impossible for them all to be his children.
What about Henry? There are only four people listed in the family. I think Herny was Johann Hermanus Frevel, who was listed seperately. He may have been an oldere child, or a brother of Issac or other relative. There is noindication that he was morvaian. All indications are that he married in Philadelphia before going to VA. He most probably dropped his spiritual first name as it appears most people did. Henry looks like a good choise given the middle name who's meaning I can't find.
I live in Florida so have difficulty searching records in PA but I suspect that a search of Church records in Northampton and Lehigh County would turn up additional facts to support this theory.
Any one have ant thoughts on this?