Do you really need to ask questions in such a straightforward fashion?
I wouldn't say anything like "I want to be sure I respect the skills of my coworkers." because, honestly, if I were an interviewer, I wouldn't like it.
It's always about compatibility. You can think something along the lines of "I don't respect him because he didn't give me the right answer", but I don't think you should put it that way. Even if you think there's a right answer, even if there really is a right answer, it's always nicer to think of things in terms of compatible or not compatible rather than right or wrong. Showing the latter attitude can be off-putting.
That's why I agree with others who say that you should try to find out the information you need less directly. Ask about the way they do things, to see if their way of doing things and your way of doing things are compatible (even if what you really want is to see is their level of competence).
Also, you can search for the information online, maybe talk to some people who work in that company.
Having said that, you could ask your question if you can afford to do so (because you're a programming superstar or whatever) and if you're looking for an environment in which you don't have to be tactful and in which people like questions like that. But, if all you really want to know is how much technical skills they have, there's no reason to ask your questions in such a direct (and perhaps slightly impolite) manner.