I've been reading some excellent fantasy novels set in Ireland. Some of the names I suggested are from those novels. They are:
Merrick Liam- It's a solid combination. I'm not the biggest fan of Merrick, but it's not bad.
Callen Thomas- I think Thomas is a nice MN for Callen. But some other thoughts: Edward (or another 'Ed' name), Miles, Ambrose, Emrys
McCoy- Not much of a mcfan of this name (Makai or Cormac are names I like though that have some similar sound qualities). But as some middle name options for McCoy: Edward, Edric, Alton, Donovan, Flynn
Zealand- I think this may be my favorite of the four FN options, it's kinda cool (though I'd personally prefer Leland or Roland). Some MN options to go with Zealand: Thomas, Paul, Saul, Miles, Clay, Brant
I like Merrick Liam best. Callan Thomas is also nice. I see the appeal of McCoy but I think the McC would be too annoying to live with. Its way too surnamey (I had a McM maiden name and never really liked it.) For some reason, the Zea of Zealand makes me think Girl name, (like Bea or something). Zeland? Leland? Oh well.
That said, Zealand McCoy is a cool combo if you're struggling for middle names (and want something cool and unique). However, I'd put 100 votes for both Merrick Liam and Callen Thomas. Good Luck!