If you're using SRDF/S (Synchronous), or SRDF/A (Asynchronous), the replication target devices are consistent, but in WD (Write Disabled) state. That indeed qualifies as read-only, so a host connected to them will identify them, but not much else can be done with the target devices in that state. Especially since they continuously update their data from the source devices. For SRDF/S and SRDF/A only when you failover, or swap, the target devices take a RW (read-write) state.
If you want to operate SRDF where both sides are in RW state and replicate in both directions look into SRDF/Metro. It makes the SCSI personality of both source and target devices look identical to the host(s) when they are in sync, both sides are RW, and writes are replicated in both directions.