Can't help with the McMillans although we knew about the name change. My wife's grandfather was Herbert William Fankhauser, an older brother of Oswald Traugott, son of Frederick Traugott and grandson of Johann who arrived in Australia in 1850. Herbert also changed his name, in 1916, to Franklands. I'm currently working on the family history including the saga of the Fankhausers in Austria and Prussia (now Poland). Happy to answer any questions.