There are profiles for this Rohrer family going back to Germany in 1615. From Johannes Michael Rohrer b. 1701 back 3 generations to 1615 were created by the import of 2 different gedcoms and were very bare bones with little or no clear sourcing. I've been working backward beginning with Johannes' daughter Magdalena to improve biographies and add sources. I doubt she actually is his daughter, but that's an issue I probably should take up with the manager.
While working on Johannes, a question arose that puzzles me, though at this point it's just a matter of curiosity. According to his profile and earlier ones, he was born 1701 in France, was 24 when the family left for the Netherlands, and just 4 years later emigrated to America. The earlier profiles show both of his parents as born in France and his grandfather and great-grandfather in Germany. (The wives of the latter two have no birth places listed.)
What puzzles me is why a man with that history who was 24 before his family ever lived in The Netherlands and only 28 when he came to America leave a will that was written in High Dutch. For his emigration to America, see the Ancestry Sharing Link in source 1 on his profile.
As to Magdalena, Johannes' will names his wife and three sons but no one else. Furthermore, both her parents died in Lancaster County, PA - one in 1772, the other bef. 1788 - while she married a man in Washington County, MD roughly about 1768, and no evidence has been offered showing her husband having lived anywhere in PA.