G23 I call my brother, son, and grandson indiscriminately by one another's names.
I think it may be because my brother is a lot younger than I am, and I was a teenager when he was a toddler. I was almost a third adult in the house, and I got in quite a bit of practice which came in useful when I had my own children, so my relationship is quite similar to that with my son. Having established the confusion, it then carried on to grandson.
I have not descended to MiL's level, though. She often called her sons by the dog's name.