relative clause agreement

[Unregistered]

which one is correct



alex is one of the employees who works 24 hours
alex is one of the employees who work 24 hours



alex is the only one of the employees who works 24 hours
alex is the only one of the employees who work 24 hours

[MikeNewYork]

which one is correct



alex is one of the employees who works 24 hours
alex is one of the employees who work 24 hours



alex is the only one of the employees who works 24 hours
alex is the only one of the employees who work 24 hours

The first two are both correct, IMO. It depends on the focus of the writer.
The first (singular verb) focuses on "Alex". The second (plural verb) focuses on "employees".

In the second two, the word "only" clearly places the focus on "Alex". I would only accept the singular verb in that case.