One of the most important tasks for a manager is to clarify who is going to do what when and why that is so important to be done well.
In the absence of clarity a great deal of time and energy is wasted.
Once you clarify who is responsible for what then stick with that person. Don’t swoop in at the last minute and take over the role or put someone else in the role. Every time you do that you lessen the person’s dignity, self-esteem, and trust in you.
Clarify what each person is responsible for and then let him or her do the job.