Jericho
When you say John and Mary Ann had died by 1851, was this before or after the census?
I think I have found the family in 1851

John Snr not there so Mary probably would show as widow on the original image. Surname horribly mistranscribed ...surprise surprise! Dewar to Adrurer:
Mary Adrurer 56, b. Montrose, Forfarshire (b. 1792-96)
Janet Adrurer 30, b. Edinburgh (b. 1817-21)
John Adrurer 23, tailor, Old Mildmin (meldrum?), Aberdeen (b. 1827-31)
Jean Adrurer 20, reeler, b. Perth (b. 1831)
Sophia Adrurer 18, reeler, b. Dundee (b. 1832)
Alexr Adrurer 14, scholar, b. Dundee
Robert Adrurer 13, Revcas (occupation?), b. Dundee (b. 1836)
Thos Adrurer no age or birth place showing on the index
Address: 28 Princes St, Dundee, Angus
The birth years I've put in brackets correspond to their entries in the 1841 census index, as you can see, a good fit. Something has gone slightly array on the transcription of the entries for Alexander and Thomas, you would have to look at the original image to determine what their individual entries should actually be.
Phew, that was bugging me! I know Joe has also put the time in trying to find them also. Team effort

If it's not them, I think I'll

Regards.
Monica