Alexander Goodwillie is on the 1891 and 1901 Scottish census with his parents. Two older brothers were born in the U.S. and 3 year old Robert (1891 census) was born in Scotland as was Alexander. Ellis Island has the image of the families return to the U.S. in 1906 at the port of New York. Alexander is shown as Alick.
Since the family returned to the U.S. and Alex only married when he was 35 and Mary Ellen emigrated in 1914 the marriage record is most likely in Michigan. I can't see Alex in the 1920 US census.
Have you checked out the FindAGrave site for Mary Ellen's tombstone? RunKitty found a great resource for you as it gives details of Mary Ellen's family and a wonderful photo of her mother. Rhodina seems to have used Rhoda and Alexina became Enid.