Hi,
I don't have any idea about how you have setup the security but if you want to separate the customer group and they only see there reports and customer admin only can delete/schedule there own reports then it is possible.
Users can see the reports scheduling instances by reports folders or Instance manager.In this case let say customer A reports are under A folder and if you provide access only to customer A group on A folder then customer A only can see the folder A.If you give the access to same group on CMC application then if users use the instance manager there they can only see the customer A folder.
Try from side to setup this kind of access and see if it will work.
Amit