I know I found out the below info from a distant relative over here.
Nice to hear from you.
My family connection to the nihill's is distant but nevertheless interesting.
My paternal great grandfather was John Regan, born 1832 in ireland and died 1893 in victoria, australia. He had a sister Margaret Regan (1824 ireland, to 1906 victoria). Margaret married Michael Nihill (1829-1901) and you probably know the rest.
John and margaret regan (was O'regan, but they dropped the O) must have come to australia for the gold rushes in the 1850's. They were the children of John O'regan and Anne Hallinan of Co Clare, Ireland.
John Regan married Anne Downes in Australia. They had a son John (1875 -1964), who in turn married Agnes Dunphy and had my father James Patrick regan in 1921.
Hope that fills in some gaps.