Regarding Mary Ann knight Erskine Rae

...
What I would is go to the free census site and start with something simple like Mary Rae. We know she was born around 1830 as a guess based on her marriage in 1853 so we put between 1828-1835 in the birth column,
https://www.freecen.org.uk/search_records/5a1405f6f4040b9d6eeac892/mary-anne-rae-1841-aberdeenshire-old-machar-1831-?locale=enWe know she's in Aberdeenshire specifically Old Machar ....so we scan for that. Now we find her , her parents and siblings and glean clues.
So then we break it down:
Alexander Rae -Journeyman Machine Maker lives with wife Janet (note OUC which in this case means not from Aberdeenshire) and children. All living at Woodside.
Mary Ann Rae and Andrew Logan have a son Alexander born 16 Nov 1855 ...so that adds credence.
Next i'd nip back to SP site and plug in Alexander Rae under old parish marriages.... change it to search Old Machar and add spouses name Janet:
ALEXANDER RAE
JANET MCDONALD/
17/07/1824
168/B
160 137
Old Machar
Now you know Janet Rae's maiden-name (though this is preliminary and needs judicious scrutinizing)
To find either of the parents birth I would start by minusing 20-35 years off the date of the wedding and look on SP site set first for Aberdeenshire. Then watch for Old Machar but they could also be close by. Some names are harder to find because they are so common.
His census age said 35 in 1841 so born about 1806. This is just a guide as census ages are often wrong, sometimes badly. So I'd start looking for Alexander Rae in and around 1805/1806. You can search between two ,so I'd set this back a bit on each side ... 1800-1810 (ten year blocks are good). There we see one in Old Machar...
ALEXANDER RAE
father:
JOHN RAE/
M
09/01/1803
168/B
110 244
Old Machar
Then comes the fun part of cross-checking everything.
Hope this was somewhat helpful!