may I add the two ways jumping into my mind if I think about communication with PN/DP CPU.

1. S7-Communication. The CPU you are about to use is able to handle S7-Communication over Ethernet (well with the CPU it is called PROFINET). This way you can use PUT / GET or BSEND / BRECV functions in both directions.
Please be aware that it is very useful to have all 3 PLC’s within one project in this case.

2. Open Communication with ISO on TCP, TCP or UDP communication. This way you can use the so called T-Communication of the CPU Ethernet interface (sorry PROFINET interface) to transfer data between the three PLC’s. Personally I would use the ISO on TCP in this case because it is more useful especially if you have dynamic data sizes to transfer.

These are the two ways I would think of.

Best regards