First, recognize that nothing more stress-inducing for may people than uncertainty - as humans we tend to run away from ambiguity. You can do this by honoring the insights and data that people have brought so that they know that there is . Explain the process and acknowledge that there will be times when they will be uncomfortable, and that it is ok, normal, and necessary.
Recalibrate timing and effort expectations to 60% problem definition and 40% problem solution. Guide the team to develop low resolution prototypes to learn and iterate with. Have the user experience integrated in testing of early ideas to further developed ones. When you will guide teams through ambiguity into prototypes, they will grow to understand that ambiguity can be powerful and doesn't last forever.