"우리 할아버지께서 퇴직을 하셨습니다."

Translation: Our grandfather retired.

[Dracogriff]

우리 should be interchangeable with both "My" and "Our".

[RQZ.Sash]

In other threads, someone said to mean "our", 우리들 is more likely to be used to avoid confusion.

[jinyoungwon]

Can someone explain “하셨습니다”?

[_SUSHMA_]

Why 'My grandfather has retired.' not accepted?

[dzeran]

Why does "has retired" work?

[wintertriangles]

It means the same thing.

[Shaxton]

"My grandfather is retired." is also accepted.

[kay45100]

What's the 께서 for?

[cin.susanto98]

It is a suffix used for honorific. You can see the explanation in Honorific Lesson