You can create a subset (or nested subset) in a sheet set.

To create a subset, you use the CreateSubset method of the AcSmSheetSet object. The CreateSubset method creates an AcSmSubset object.

After an AcSmSubset object is created, you can add sheets to it. Create an AcSmSheetSet object and use the AddNewSheet method or the ImportSheet method. If you use the ImportSheet method, you create an AcSmNamedAcDbObjectReference object with the appropriate file name and layout name. After calling the ImportSheet method, you must call the InsertComponent method to finish the import.