The 19 year old Robert DOUGLAS Sr in Simonds in the 1851 census may not be yours. That is all one household... John DOUGLAS is the father who came from Scotland in 1833 Thomas DOUGLAS is his 11 year old son b. NB Matilda DOUGLAS is John's 10 yr old daughter b.NB John M. ROONEY is John's son-in-Law ( m. Margaret DOUGLAS 17 Feb 1851) Margaret is listed next and came in 1933. Then the 19 year old Robert is listed and he came in 1933. But the censuses are full of mistakes so he "could" be yours. The part that says they all came in 1833 is very crucial though. Robert Jr's death cert doesn't indicate that.
According to his death cert. your Robert jr was b. 5 Jan 1853 in NB. and his father Robert Sr. was b. in Saint John, not Scotland. Mary CAMPBELL's birthplace is not filled in.
Maybe yours were living in Portland in 1851 - the part of Saint John next to Simonds Parish and the census records were destroyed. It's the largest part of Saint John.
There were several Presbyterian Churches there. St. Matthews Pres. Ch. on Douglas Ave., St. John Pres. Ch. in uptown Saint John and now allied with St. Stephen Ch. These are all within 3 or 4 miles of Coldbrook where they lived when Robert Jr. died in 1920.
In the 1881 Simonds census, Robert Jr. is listed as "Robert F. DOUGLAS age 27, b. NB, Church of England, Farmer. He was listed as a Farmer on his death cert. 1920 too. Annie his wife is listed as Anny age 35 b. NB, Church of England. Under the ethnic origin, Robert is listed as NB and Annie is English. They have a dau Elizabeth age 1.
In the 1901 census he is listed as Robert "DUGLAS" (mis-spelled by census taker) b. NB, 12 Jan 1854 Church of England and ethnic Scottish, Farmer. Annie is the same as 1881. Children Lizzie b. 24 Jun 1879, son William b. 30 Sep 1881 (Birth Cert. 24 Sep 1883, Coldbrook) dau Vina A. b. 30 Nov 1888 (birth Cert. Vina Alice 30 Nov 1888) and dau. Janey b. 15 May 1892. (Birth Cert. Jennie Alma b. 28 May 1892, Simonds)
Jennie Alma DOUGLAS m. William ELLIS 2 Nov 1911, Saint John Co.
I forgot to mention Annie FUDGE was d/o James FUDGE (b. England) and Anne MURDOCK (b. Saint John)
By the 1911 census Robert gives the same birthdate as 1901, Annie b. March 1861. Janey is now "Jenny" b. May 1892, Wm. b. Sep 1893 and no more.
Violetta Viney DOUGLAS d. unmarried 21 May 1959 age 70, b. Latimer Lake which is on the Loch Lomond Rd.
William Georeg DOUGLAS d. 5 May 1961 b. Lakewood ( same area) on Loch Lomond Rd. leaving wife Daisy B.and son Wm. J.
Elizabeth m. Frank A. HICKS and d. 27 Jul 1935.
All are buried in Fernhill and lived on the Loch Lomond Rd or a side rd.
As for your quest for parents Robert DOUGLAS and Mary CAMPBELL, I can't find anything on them,sorry.