American living in AUS here. I spell it Mom, pronounce it mum, say "mam" as an amalgamation of mum and ma'am when I'm in a hurry, and reserve the term "mother" for when I'm whining or being sarcastic.
Dad is dad, unless I'm trying to get his attention, in which case it is appropriate to turn it into a two syllable word with an "uh" after the last d. Dad-UH. If I'm calling for him I usually do the thing Crow does in MST3K where he says it like, "Dahd? Dahhhhhd?"
I call them by their given names when talking about them to other people, or when trying to get their attention in a loud room/large space.
EDIT: Also,