Redmine

Hello. I am planning on using redmine at my work. We have lots of projects and something around 30 people. The current process of demanding a task is too slow, because the project leader has to write the demand down, that goes to the operational sector, that allocate that demand to someone, then it goes back to the project leader. With that person selected, the project leader can then go to the person and explain the task.

With redmine, we want to the following: when the project leader creates a task, he already indicates the person he would like to get it. He can look in the Gantt chart to see if the selection is really available. And then, there's a few people able to double check that demand, meaning: They have to approve the request, and if they don't approve, select a substitute. By that moment, the selected person receives the task and an email with it.

How can I do that kind of approval system?