The Thomas A. Mylroi quoted in the 1891 census fits the the right age but he appears to have started out as Thomas A. Corlett, November 30 1882. His age in Ellis Island records is 24 years 7 mths.
Isabella Corlett eventually married widower Robert William Kelly Jan. 1891.
There were five others from Lonan with Thomas A. Mylroi on his journey all heading for the mining in Bisbee Arizona and a meeting with James Christian, but none that appeared to be a brother.
He appears to have adopted his fathers name after christening so there may be another half brother with different surname.
The name McCosker would be unusual in the Isle of Man