Initialize IWDG with two difference handles
There is only one IWDG peripheral.

If you want to share the HAL instance of the IWDG you have to link the handle across compilation units with the extern keyword.    

Or use the IWDG registers directly.





Also, the design of sharing the IWDG smells, you may want to reconsider the design here.
http://www.ganssle.com/tem/tem365.html
http://www.ganssle.com/item/great-watchdog-timers.htm