Answers to your Questions:
Q What was the address of her 1871 birth - and was her mother Sarah the informant of the same address?[/color]
A Sarah was informant, both addresses given as Providence St, South Lynn
Q What was Sophia's 1890 baptism address & occupation (of the father) given as?
A Baptism only from FamilySearch so far - these details not provided
Q Who did Sophia marry in 1891 (McCLEN? or ALLAN?), and what was her address at the time? Have the marriage witness' been identified for possible clues?
A Sophia married Patrick ALLAN - the witnesses were William Brown and Sarah Brown - amended on the form from Borley! It seems Sarah was 'married' to WB in 1901 & 1911 though no BMD confirms this - suspect they were unmarried partners which at least lasted from 1891-1911+
Q What are Sarah's Census details (and that of her household) for 1901 & 1911?
A You have the correct details fo Patrick & Sophia's family - I've photoedited and compared the scripted occupation and pretty sure it reads 'Finisher' - he was always recorded as Caulker/Rivetter previously
Census Records for Sarah:
1901
26 Church St. Walker, Newcastle
Head: William Brown, 36, Shipyard Labourer, b. Newcastle
Wife: Sarah Brown, 36, b. Essex
Adopted Son: Peter Allan, 11, b Newcastle
1911
Lock-Up Shop, 26 Church St. Walker, Newcastle
Head: William Brown, 44, Sailor, b. Newcastle
Wife: Sarah Brown, 44, Housekeeper b. Kent, Tunbridge Wells
Grandchild: Peter Allan, 21, Arrchitect's Clerk b. Newcastle
Grandchild: Sarah Allan, 14, Domestic b Newcastle
There are no marriage details given on the original transcript.
Well you did ask!!
Sarah seems to be creative with her age but going from Sophia's MC (where is 19), assuming Sarah Brown gave birth at 16 she would be 35 when she was with William Brown as witness, 45 in 1901 and 55 in 1911. I have taken her DOB as 1856 on this assumption.
So just where is Sarah BORLEY b. 1856 Tunbridge Wells, Kent? or maybe Essex is the birth location