Translation:Good morning, Grandfather.
Usually, おじいさん is written with the kanji お祖父さん when used to mean "grandfather" (as far as I can tell).
Yes. But unless you are a child, he might get offended and says "I'm not your grandfather! " I would say to my own grandfather, おじいさん、おはようございます。I say first おじいさん、only when I need to get his attention.
I put 'Good morning, Grandad' and it was marked incorrect. 'Grandad' is a correct spelling, this should have been accepted.
So one question told me おじいさん was grandfather and then another told me it was uncle