That the family was in PA that far back indicates it is not a Jewish name. It was probably German / Dutch, which often sound similar to later period Jewish names.
This is also indicated by being Lutheren, that being the main Protestant religion in the northern section of the Germanies of the time.
While there have alwasy been a small number of conversions, that doesn't prove anything for a specific family.
DNA testing, as mentioned by the other poster, is probably the easiest.
Otherwise, I suspect you'd have to find an adult baptism record prior to marriage into the family line. That will be tough I'd think.
A slim option would be habits and rituals that are done, often with no idea why, but are of Jewish origin and not Christian. For example, lighting two candles every Friday night. Or never eating milk and meat, two sets of dishes, or never eating pork.