I'm not sure what your question is. If the second witnesses do not say that the first witnesses were with them and thus could not have been at the scene of the incident, then they do not qualify as Edim Zomemim. The Torah's Chidush of the law of Edim Zomemim is that the second pair of witnesses are believed only when they say that "at the time that you say that you were in a certain place, you were in a different place with us." Any other contradicion of the first Edim does not constitute Zomemim. (The Gemara (5a) discusses why we are not concerned that perhaps the first witnesses went from one place to another on a high-speed camel.)

D. Zupnik