Dear NT:

You wrote:
> John and Harry can repair our car.
> Our car can be repaired by John and Harry.
>
> Do these sentences mean necessarily that they can repair it if they work
> together or could they mean that each of them can repair it alone?
>
While either could make sense in context, normally it would mean that the two men working together could repair it or, most likely, the two men normally would work together (e.g., partners who own a repair shop). And is the same as a plus sign.

If you wanted to say that each could repair it alone, then say so: “Either John or Harry can repair our car” or “Our car can be repaired by either John or Harry.”