What is the difference between tapadh leat and tapadh leibh?
Tapadh leat is singular; tapadh leibh is plural/formal :)
leat = familiar singular
leibh = plural / respectful singular
So wouldn't it be more normal to say tapadh leat to a close relative?
It's culturally considered more respectful to use "leibh" for any relative who is older than you, even if they are very close, like parents or grandparents.
It's always father... any chance this Q could ring the changes?