I have a Mom and Dad.
I also have Grandmas and Grandpas... collectively, they are my Grandfolks.
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Grandparents just seems too formal to use for them.
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To differentiate, I use their last names (so Grandma Smith or Grandma Jones). When we went to visit them, we said we were going to 'the beach' to visit the set of grandparent who live on the beach.
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The other set was referred to first by the town they live on, then the street they lived on when they moved so we remembered to go to the new house.
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Usually, when writing, I call them G'ma and G'pa or G'folks and I call myself their Grand-baby.
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On a funny (kind of related) note, my brother's wife came into the marriage with a puppy, so I decided my brother is a 'dog-father'.
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