When I first saw
Malachi's name, it was spelled as
Malachy, but various researchers on this line seem settled on
Malachi. They probably aren't namenerds and may not realize Malacy is a separate, and Irish, name. I haven't seen any offical documents yet, not that spellings there can be taken as etched in stone either. I do prefer
Malachi, but I'm quite open to
Malachy as well.