Mom is mom
Dad is "fat man" - this is a nickname he got when I was just starting high school. Not really even sure how it started. I called him that once at church after everyone was filling out and I got a couple people give me weird looks. A couple had "horrified" looks on their face. One of the older ladies asked me about it later and I explained it was a nickname and that calling "dad" across the room would have had 200 people looking at me.
We also do the Marco/Polo thing in the store, so we all look like complete idiots, its just the kind of family I grew up in.
I had a great grandmother who was "grandma odie" because we could not pronounce "zoe"