How many co-authors are enough? I am doing research in an industrial organization. Now, I have written a paper describing my work and outcomes. The idea was completely envisaged by me and the paper was written solely be me.  It was an outcome of a funded research project, but the research done was no where in the scope of the work, and I managed to squeeze time to do this work. 

Now, I am confused on whom to include in my co-authors lists. 
I have only one teammate, with whom I worked in the project but didn't take any help for doing this area of work and writing the paper. But I think he deserves to be a co-author since we discussed various related things. 
I also gave the paper for review to my reporting officer who gave a few grammatical suggestions and tips on paper writing.

Now, the problem is, I have two more level of hierarchy above my reporting officer one of them being the director of the organization. Would it be ethical to include their names as co-authors when no discussion was made with them regarding this or should they be acknowledged ?
Note: The usual practice in my organization is to keep your superiors name before yourself(some red tapism probably), and I have already violated that by keeping myself as first author(thanks to ASE).
People who have made no intellectual or scientific contribution to a paper should not be listed as authors. So, unless your upper-level supervisors have had an active role in designing the project, carrying it out, or writing the papers, they should be excluded. This is the practice normally carried out in corporate environments.