Finding the 1880 Union IA census...
as you, I am not finding anything else in census to uphold this family.
I do know that there is a family tree that offers the names of children, along with dates of family, but not finding collabarating evidence.

Martin Brenna 1840 Cork, Ireland died 1889 Omaha nb
Hannah Barrett 1840 Ireland, 1886 NB
children:
John 1860, Pat 1863, Mary 1869, Ellen/Nellie 1870-1919, william 1863-1863, Lizzie 1868, andrew 1870, Martin 1878