Robert Muir's parents are a brick wall. Recently, I signed up for a subscription to MyHeritage.com. Two people have "my" Robert Muir in their trees with parents listed. One person was unsure where she had gotten the information about Robert's parents but thought perhaps it came from her great aunt , who I believe descended from Robert Orr Muir, a son of Robert's.
Another sent me the following infographic from a book compiled by an Australian branch of the family, which would likely be the descendants of Henrietta (Muir) Williamson, a daughter of Robert's. They believe "my" Robert was born in 1803 in Flemington and was a brother to Andrew Muir, making their parents Robert and Margaret (Melville) Muir. Yet, the scant documentation I have -- the 1841 and 1861 census and death registration -- state he was born in Ireland about 1800 and that his father's name was James.