The Ridley childrens' mother is Elizabeth Bulman's older sister Ann. I think you might be right about Thomas Bulman being misnamed Ridley, with a ditto surname under the other grandchildren on 1861.
1881
Ann Ridley 64
William Ridley 30 Son
Walter Bulman 56 Brother
William Bulman 54 Brother
Elizabeth Lawson 50 Sister
George Lawson 54 Brother in Law
George Lawson 11 Nephew
Walter Hills 6 Nephew