Sometimes troubles seem to come along on top of one another and it all gets too much.
I agree that your DH needs to see the GP about his nocturnal terrors and wanderings. It could be a symptom of something else, or it could just be that he is anxious. I used to sleep walk but I don't think I do any more and my DC have had night terrors when they are worried about things - none of us remember!
You could try to persuade your DM to take the advice of the eye specialists, but as for cleaning etc, I wouldn't get too wound up about it, you can only do your best to make sure it is not too unhygienic.
Can your DH help you catch the cat and hold him while you treat him? Can he be tempted by something?
Best wishes, don't get too stressed - stress is not good for you! 