BrE: has (individually)/have (collectively)
Grammar Girl :: Collective Nouns
Our staff has/ have worked hard.
Which verb should I use?
I've gone through the link. However, if I am not wrong, 'staff' is not listed there. I may be wrong.
Below are the definitions and examples of how to use the word 'staff' (from Collins Cobuild Dictionary).
The staff of an organization are the people who work for it.
The staff were very good...
He thanked his staff.
...members of staff...
People who are part of a particular staff are often referred to as staff.
10 staff were allocated to the task...
If I am not wrong, for one person, it should be 'staff member'. I stand corrected.
You just have to use your best judgment, and even though this seems tricky, the good news is that you can never really get it wrong because 1) there is no real rule, and 2) you can always just assert that you were thinking of the couple as individuals (or a unit) if someone questions your verb choice (2).