Hello Gossamer,
I am not an Agnew but do have a connection through the brief marriage of Eliza Ann Elliott born c 1839 to David Agnew ( father, James Agnew) on 13 Nov. 1866 in Raloo, Antrim. Eliza's father, David, was a Kilwaughter farmer.
They had a child, David, b 14 Jul 1867, registered in Carrickfergus.
Unfortunately David Agnew snr died in the year of his child's birth at only 26 years of age.
Eliza Ann remarried in 1871.
This information may help with your Agnew jigsaw.
Regards,
KiwiRose