To avoid each ministry schedule from being seen by all of your volunteers, create separate schedule posts for each ministry.
When saving a schedule, choose the option to "Customize the online layout..," or to create an additional Live Schedule Post, from your open schedule, select "Create additional Live Schedule Posts..."
In the "Online layout and options" window, click on the "Included Ministries" heading on the left and click on the ministry/ies you wish to include in this post, then check the option at the bottom that says, "Only show this schedule to volunteers in the included ministries" and click the Save button. This will make the schedule viewable to only volunteers in the ministry. Repeat for each ministry/grouping of ministry schedules you wish to create.