Dear Prabhu Very good Morning
First cumming to 2nd requirement . it is possible in sap sd standerd also
Just do this settings Use BOM Concept here Manually maintain discount in vk11 after configuration CS01 ( main item and sub item )
3RD requirement is If you are using BOM Scenario And in free of goods it wont work
1St requirement: this is very interesting I dont think so it is possible in sap stranded