For me it's not obvious, what your set-up is supposed to do. For an example ... why run the Keystep through the A4 anyway, if you want to control the OT with it, but the A4 shall be master for the OT too?
Since the A4 shall be the master, I assmue it shall be the center piece of the set-up and be master-clock and master for start/stop, MCC etc. and it's not "controlled" by an other device. Is this right?
If the Keystep shall control the OT only and not the A4 too, it would be better to send it's midi directly to the OT. If the A4 shall be master-clock and master for start/stop etc. for all boxes, you could patch the following midi routing using your midi-merger:
A4 midi-out --> midi-merger-in (sends midi, midi-clock, and midi-start/stop etc. to the network)
Keystep midi-out --> midi-merger-in
midi-merger-out --> OT midi-in (OT receives now midi from both units and clock etc. from A4)
OT midi-through --> Keystep midi-in (sends clock, start/stop from A4 to the Keystep)
Now all boxes are syncronized and you have only to set-up each box, that it sends/receives midi as wanted