Bore them to tears with as much detail as often as possible. Trust will build. Be honest about the realities and future expectations. It is not uncommon for a series of changes to occur during the process of readjustment. If people begin to relax their guard only to get more shocking news, they will be much slower to trust any statements in the future.
Empathetic leadership is far more effective than being a threatening autocratic boss.
Certainly some things need to be pushed, but during the traumatic transition period, don't focus too much on efficiency, mistakes or poor attitudes. Instead spend your efforts in coaching and encouraging people to be successful in bridging the gap between the old and new. Reward each success and let the ones who adjust more quickly be examples for the struggling members of the group. Remember that personal strength and strong supportive relationships are often forged in the fires of adversity. When the crisis has passed, many people will be surprised by some of the skills they exhibited that they would otherwise never have realized.