I don't know anything about the Miller family, my Schumachers married into the Baker and Virts families. I am pretty sure that your George Schumacher was the grandson of Rudolf Schumacher, and the son of George Schumacher.
Rudolf was born 1693 in Kleeburg, Elsasse, Germany and immigrated about 1749-1752 through Philadelphia. 3 of his sons came on the ship "Christian" in 1749, and I believe the others followed with the father and the sister Juliana later. No mention of a mother has been found. Some of the brothers stayed in PA, while Rudolf and Juliana and some of the brothers moved into Frederick Co, MD until he died about 1767. His son Philip also died in Frederick Co, MD in 1776, but I am pretty sure that Juliana and the other brothers who went to MD had moved on to Loudoun Co, VA by then, as her son Samuel Baker was born in Loudoun Co about 1770. One of the brothers, your ancestor George, was born about 1737-1739 in Salzburg Germany, married Anna Maria Barbara about 1758, presumably in America, but not sure where, and became a deacon in the German Reformed Church, Presbyterian branch. He died in 1808 in VA, probably in Loudoun Co. You might look for records of George (Sr.) in the church records, but be aware they are probably written German. That is what I found for the Lovettsville records, although I don't think their church was the Presbyterian branch. Many of the Schumachers attended the New Jerusalem German Reformed Church in Lovettsville, so you might look up those records to see if you can find George Sr. or even George Jr. there. Let me know if you need the microfilm number for those records. Your George Schumacher, son of George (Sr.),
was born 5 Feb 1772 in VA, married Margaret Miller on 30 Apr 1796, and died about 1821 in Armstrong Co, PA. He was about child #6 of 9 for George (Sr.) and Anna Maria Barbara.
I have info on his brothers and sisters if you want it. His youngest sister Christina Schumacher born about 1781 married Moses Miller on 17 Oct 1799, and he was probably related to your Margaret Miller. You might look for a marriage record for Moses Miller and Christina Schumacher or Shoemaker as they may have spelled their name by that time. It is quite likely that Moses Miller was Margaret's younger brother.
Good luck, and let me know if you want more info about your George's family, I just don't know anything more about the Millers.