since you have 2 workstations decide which one will be the masterkeyboard for the mpc (which one assures you the better performance?)...
then put the midi out of the selected keyboard into the midi in of you mpc. after that you put 1 of your 4 available midi outs of your mpc into the midi input of your fantom and anotherone of your 4 mpc outputs into your triton midi input.
if you did this you go to your two keyboards and set the "local midi" function to "off". then set the two boards as "slaves" in their midi preferences. next go to your mpc and set it as "master" midi device in midi preferences.
now, the reason i told you to turn the local midi off on the two keyboards is because otherwise everytime you would press a key on your masterkeyboard it would send a "midi note on" message to its own sound generator (triton or fantom) [this is why the local midi function should be on if you use you workstation standalone, otherwise you wouldnt hear anything]
BUT what you want to do is this: send a midi note on message from your selected masterkeyboard to the midi input of your mpc and trigger the sound generators of your two boards through the mpc midi outputs. if your mpc midi output A goes to triton then set the track type inside the mpc to MIDI (instead of DRUM) and select A to trigger the triton sounds, if your mpc midi output B is going to the fantom then set the track type inside your mpc to midi and select output B to trigger the fantom sounds. you have to assign the channel also.. for example: if you have chosen a string sound which is on the 4th channel inside your fantom mixer then use output B4 (can go from B1 to B16) on the particular mpc track to trigger the string sound. be sure to be in performance mode (sequencer mode) inside the fantom and triton.
this is basically it... theres always a few things you have to get around but if your get around them once youll be fine... try it and see if it works,