My MIL is Granny, she was Granny to her first grandkids before mine were born so she was always going to be Granny, she also HATES Nanny (common, innit) anyhoo, my daughter started to call her Nanny because it's obviously easier than Granny for a toddler to say, but then MIL would correct her.... which resulted in her going through a a phase of being called NannyGrGr !I thought one of the joys of grandkids was the names they came up with for you.
My kids called my parents Jonjon and Mygranny ( Always one word. Granny on its own was utterly unacceptable). The in-laws, who I have to stress were bloody lovely and two of the nicest, kindest people I’ve ever met, were Fanny and Grumpy.