Very strange indeed on Elizabeth's 1884 death. Like you I did the same searches you had for Elizabeth's death the other day and could only see the two you found. Tried again yesterday and up came the other 1884 entry!
In any event, you have found her death entry

Regarding Donald 1842's death. As you have seen, you have to keep on referring to and finding possible events to try and narrow down years when things could have happened.
We know Donald Snr had passed away by the time son Ewen married in 1897. I am pretty convinced that the 1891 census entry with 'wife' Magdalene is him stilll alive:
D Macdonald 49 Retired Station Master b. Alvie
Maudline Macdonald 36, wife b. Rafford, Morayshire
Erven (?Ewen) Macdonald 18, clerk b. Dall (?spl)
Mary Macdonald 12 b. Dyke, Morayshire
Mary Macdonald 4 b. Dyke, Morayshire
Address: Railway Ter No 2, Nairn, Nairnshire
So we have a six/seven years likely range for his death. The search I did yesterday was for a death between 1891-7, for a Donald b. 1842 +/-1yr (I have only used 1 year variance as he was pretty consistent with his age) which showed 9 deaths. If I had to close my eyes and chose just one to look at

, with the info we have as a guide, I would consider looking at the one I mentioned yesterday that seems to have taken place in Nairn the same year of the census, 1891. If it is not that death, then you are left with 8 more as possibles...
Monica