I stumbled upon this website (accidentially, I admit) and read your note and wanted to respond to your inquiry. There are definitely two different lines and LAHEY is one of them. I really know very little about the history but know that you will find LAHEY in Canada,specifically on the east coast...like Nova Scotia, Prince Edward Island and New Brunswick. The name is pronounced in two distint ways as well...LAY-HEE as in the same pronounciation asLEAHY and LAH-HEE with a silent a (with perhaps a bit of a slang on the a)
I hope this helps and good luck!
Eric Lahey ( My family pronouces our name as LAY-HEE but I have aunts who pronounce their name asLAH-HEE...go figure!)