Delphi does not natively support multicasting of events. You have to create your own mechanism for that. The simplest solution is to store your registered objects/handlers in a list, then loop through that list when the event is triggered, calling each object/handler as needed. For example:
Simulating multicast events in Win32 Delphi
Allen Bauer wrote a series of blog articles about a more advanced way to implement multicasting events in Delphi:
Multicast events using generics
Multicast Events - the cleanup
Multicast Events - the finale