husborth Answer:
this is a question of the utmost importance that requires all of my analytical power to address, thank you.
so the truth is that, the grandfather almost never picks the actual nickname, it’s the parents/children - the grandfather may insist on being called the Grandfather, but if the dad goes in and is like uh, no, we will be calling him pawpaw, pawpaw will stick. there is no agency in this choice. i am partial to luke teaching his baby ben skywalker to exclusively refer to the hulking ex-warlord in the corner as “pawpaw” because holy shit, i mean, just, holy shit. he is now Lord Pawpaw.
my second answer utilizes my own headcanons for huttese, which ‘ebi’ is the word for 'grandfather’ and this was designed to achieve the following; baby ben skywalker referring the hulking ex-warlord in the corner as “bee” or “beep.” perhaps even. “bee bee” or “beep beep.” he is now Lord Beep Beep. furthermore i’ve joked in happier AUs, the twins as babies out to call obi-wan “bee” because they can’t say his whole name, which means, in a complete fit of narrative irony, vader’s grandkids now refer to him by the same thing obi-wan’s grandkids would have. he is now demoted to Lord Bee.