I think these "IM" modules are connected via Profibus, not MPI.
Maybe the "IM" are IM153-2 or IM153-3. These are ET200M with redundancy capability.
S7-400 and/or DP i/o in a redundant configuration isnt trivial. I dont think you can rely on getting enough info in a forum like this.
It may be necessary with some real training at a Siemens training center. This training should cover also how to create a WinCC with redundancy and system messages from the PLCs in a redundant configuration.