As part of those separate meetings you should ask each employee if he or she is willing to have a joint meeting with the goal of finding solutions that work for everyone.
Avoid a fact finding mission with the goal of placing blame. You do NOT need to "get to the root of the problem." Instead simply acknowledge that there are issues that need to be resolved and then focus on solutions.
Elinor Robin, "The Relationship Mediator," has more than 18 years of experience in mediation while working within the public and private sectors.