1The latest census I can access is 1921. My mother was born in 1921 possibly a month after the census was taken. Do I have to wait 10 more years until the 1931 census or is there another resource?
A check of the Valuation Rolls and Electoral Rolls would not give you any info in respect of the family dynamics. I suppose one check might be whether to see on the Electoral Rolls whether Henry and Margaret lived together to exclude the possibility of a separation.
2. My mother was born with the surname Dickson and was the 5th daughter of Henry Dickson with no brothers. Her maiden name on the certificate when she married in 1943 was Dickson Daniels with her father as James Daniels, not Henry Dickson which suggests (to me) she was put up for adoption after she was born and adopted by the Daniels family for reasons currently unknown.
The surname of Dickson is showing as a middle name for your mother on both her marriage and death registrations. As you are likely aware, using surnames as middle names was/is common practice in Scotland. Her surname is showing as Daniels. Looks like James Daniels and wife decided to leave her birth surname as part of her name.
Formal adoption in Scotland did not start until 1930. They would have been arranged privately and there are no records available up to 1930 for these arrangements. See
www.nrscotland.gov.uk/research/research-guides/research-guides-a-z/adoption-records
5. The census date was June 19th 1921 and my mother was (inconveniently) born on June 26th 1921 and does not appear on the listing for James Daniels under the John Watson's Institution entry. To trace my history on my mother's side I have to determine whether to follow the Dickson line or the Daniels line - suggestions as to what might have led to the change of surname?
Your choice really
There are some family notes listed for Henry and Margaret's families in the wikitree linked above. This period of the 19th C should be easier to research as more records are available online.
Have you researched anything so far on James Daniels? Did he have more children, for example? Marriage showing for him in 1910 in Edinburgh. I think there were at least 4 children born to them. Birth index shows their entries between 1911 - 1917.
The fact that your mother gave James Daniels and wife Mary (Fingland) as her parents on her marriage registration does imply she was raised by them. They also show on her death registration. Not sure how to determine the reasons why though
Guessing you had no contact with her family/your aunts in later years? Your last question (6) also touches on this issue of an informal 'adoption'.
Monica