Please help me about replication set. By checking below parameters, it seems like we could have multiple targets synced with one replication source.
The new feature, Replication Sets, doesn't change the number of replication targets you can have. OpenEdge Replication and Replication Plus both let you have either one or two target databases updated by a source.
Prior to 11.7, a target database could transition to a source or to a normal (non-replicated) database. There are certain things you can automate, like enabling adding AI extents and after-imaging in the new source after transition. But the two targets have no knowledge of each other. After the failure of the original source and the transition, there is a period of time where you have a single point of failure until you set up the former target2 as the new replication target of the new source (which used to be target1).
The new feature in 11.7 is inter-agent communication, i.e. the agents of targets 1 and 2 are aware of and communicate with each other, when the three are configured as a replication set. When the source fails, target1 transitions to become the new source and target2 also transitions to become its new target, preserving failover capability.