I think that should work so long as you can configure the Nord to forward MIDI messages to the Motif. If each keyboard is assigned to use different channels, then you can control which keyboard will process the messages based on what channel you send them on. If you want to use the Midisport, it sounds to me like you are encountering the same issue - the Nord keyboard is not outputting the messages to the midisport. So there is still something you have to configure on the keyboard to ensure it forwards messages.
A surefire solution would be to have a MIDI router in between your tablet and two keyboards. An expensive example of this is the mioXM. You would have the tablet and both keyboards connected to the mioXM. You can then forward messages to each keyboard from the tablet. There may be less expensive models that you could use for this purpose as well. There used to be a mio2, but that's no longer sold unfortunately. This company sells a few models, https://www.cinaratech.com/info/shop/midi-products, but I've never used them so I can't vouch for their quality or reliability. An alternative solution would be to use bluetooth. You could have your tablet connected to both keyboards at once using CME WIDI Masters or CME WIDI Jacks.
Mike
A surefire solution would be to have a MIDI router in between your tablet and two keyboards. An expensive example of this is the mioXM. You would have the tablet and both keyboards connected to the mioXM. You can then forward messages to each keyboard from the tablet. There may be less expensive models that you could use for this purpose as well. There used to be a mio2, but that's no longer sold unfortunately. This company sells a few models, https://www.cinaratech.com/info/shop/midi-products, but I've never used them so I can't vouch for their quality or reliability. An alternative solution would be to use bluetooth. You could have your tablet connected to both keyboards at once using CME WIDI Masters or CME WIDI Jacks.
Mike