Sorry to hear he's poorly. Not much you can do differently really, if he needs picking up when he is ill then just do it, you aren't planning on rocking/walking to sleep but you can give extra comfort.
Long NW are a drag. I would expect the worst and try to plan a sleep time for either you or DH and for someone to take the next shift the following day so you can catch up with a nap at least. If he is awake but quiet or calm you can leave but if he is shouting and crying you do need to respond. If it is very long you might find it easier to grab a pillow and duvet and camp out on the floor by his cot, he at least knows you are there and therefore he is safe. You may not get any sleep at all but you may be able to rest a little more than standing/sitting in his room.
The idea of having a chat rather than just saying lie down etc may well work as he loves a 2 way chat.
Hmmm...I may have misled you with this. Caution about taking part in a two way chat and this becoming a nap/night time stalling tactic, you don't want to take part in much chat which is why the key phrase is helpful, it is a response which does not engage in conversation, but what I was meaning was that sometimes if he is really really frustrated it may be worth 'hearing' him so he knows he is heard. So for instance "yes, I know you are tired and frustrated, I hear you, Mummy is right here, yes, I know, you want out, this is tricky for you, I'm here" rather than getting into real conversation or answering questions etc.
Hmm, hope that makes sense.
anyway, you are all doing great! Certainly moving forward, only so sorry to hear he is poorly