Multicast IPC options in unix
There's nothing as conceptually flexible as multicast, but with a few limitations some of the facilities might do what you want.
Signals may be delivered to a process group. The other IPC mechanisms you list have a sender/receiver model and are not suitable for multicast, barring local extensions like Linux's multicast AF_UNIX sockets as @Barmar points out in the comments.
If you only need to send a single "signal" to descendant processes, and only once, you may use an inherited fifo. All receivers inherit the read end of the fifo but not the write end. The process holding the write end closes it at some point, and all receivers will detect EOF on their read end copies.