This example illustrates how the appointment editing form with multiple resources selection can be implemented in a project with ASPxScheduler control bound to XPO via the Unit of Work.
To switch the scheduler to multi-resource mode, set the ResourceSharing property to true. Then implement a custom appointment editing form and adjust the appointment field mapping for the ResourceIds property.
Note also how the ResourceIds property of the XPAppointment XPO object is implemented and the role of XPORowInsertionProvider class.