1930 census, Robert B. Montgomery and wife Sarah A, in Inkster City, Grand Forks, ND:

http://www.rootsweb.com/~usgenweb/nd/grandforks/census/1930/...

And in 1920:

http://www.rootsweb.com/~usgenweb/nd/grandforks/census/1920/...
(Robert last one on page)
http://www.rootsweb.com/~usgenweb/nd/grandforks/census/1920/...
(wife and daughter)

Twp 144-88, Mercer Co, ND - Ernest and wife:

http://www.rootsweb.com/~usgenweb/nd/mercer/census/1930/19-0...

and in 1920:

http://www.rootsweb.com/~usgenweb/nd/mercer/census/1920/125-...

In case you haven't got them and want them:

Robert B. and Sarah plus three daughters in 1910:

http://www.rootsweb.com/~usgenweb/nd/grandforks/census/1910/...

1885 census, should be 'R. B.', not 'A.B.':

12-020-21 Montgomery, A. B. 33 Farmer Canada Strabane Twp Grand Forks
12-020-22 Montgomery, Sarah 30 Wife Canada Strabane Twp Grand Forks
12-020-23 Montgomery, Ernest 6 Son Canada Strabane Twp Grand Forks
12-020-24 Montgomery, Ewer 4 Son Canada Strabane Twp Grand Forks
12-020-25 Montgomery, Blanche 1 Daughter Dakota Strabane Twp Grand Forks

1900 census:

http://www.rootsweb.com/~usgenweb/nd/grandforks/census/1900/...