There is a difference between Ojiisan and Ojisan. and how it’s pronounced.
Ojiisan おじいさん - grandfather
Ojisan おじさん - uncle
How it’s shown as romaji is a different story. But I’ve seen it both ways depending on if they are talking about a grandfather or uncle or older person.
It’s also the similar with Grandmother and Aunt.
Here is the link that shows the difference between the two.
https://youtu.be/0Hs-bZgRhq8