The problems you are talking are much bigger than executive vs executive issues and probably fall in the "Complaints about an executive’s competency or performa

The problems you are talking are much bigger than executive vs executive issues and probably fall in the "Complaints about an executive’s competency or performance" where Ben suggest that you shouldn't, indeed, solve this with a meeting as it may imply many actions on your side. What I can add to Ben's advices is: assume everybody lies and work on facts only. You don't want someone innocent to be slandered and you certainly don't want someone guilty to get away with it. Fortunately, this is extremely rare, unless there is something very wrong with your company.