So i have 4 xbee modules, two are s2 and two ar s2 pro.
I can create a small network with both s2 modules, and another with both s2 pro, but i cant make them work in single nework.
Here is picture where we can see configurations for corrdinator (s2) and router/ end device(s2 pro)
Try simply upgrading the firmware on your PRO module from the no longer supported Znet 2.5 code to the updated XBee ZB versions. You will find they will then communicate with each other.