Is a post doc advisor who makes superficial contribution entitled to authorship? I am a postdoc with two advisors (not something I would recommend for everyone). I would describe the involvement of my two advisors in the project I undertook as quite superficial. I met and discussed a lot with them, they gave me some useful ideas, but they didn’t contribute much to the core of the project.  I didn’t even feel they put genuine effort to understand what I was doing.  Most of their feedback was related to ideas that didn’t work or was not implemented. If the right for authorship is defined by a significant intellectual contribution, then I wouldn’t really describe their role as such. 

Is it ethical to include them as coauthors in the article summarizing this project, with an author contribution statement that describes each one’s role? 

In this case their role will be something like giving useful tips, analyzing the results, ..etc.
The reality is that standards for authorship are not universal across disciplines.  In some disciplines, your advisors should be considered authors.  In other disciplines, you advisors should not be considered authors.