On the basis of what you say, things are connected up OK, everything is playing, so really what you want to to do is dependant on you.
You don't say much about the midi data you're sending.
I would guess that you might wish to separate the midi channels. You need to check the details of the receiving devices, and see which ones can be set up to receive midi data on certain channels ONLY. Many devices can be so set, but some cannot. Then share out the 16 channels (0 thru 15) between the three devices, and set the devices accordingly. Then, revise the data being sent so that certain data is assigned to certain channels. Hence, device A plays the souds that it plays best, and so on. Some overlap may well be an advantage, will give you a 'layering' effect.
Try that, and see if that's heading in the right direction. Then get back?
Geoff.