William and Agnes can be found on familysearch.org. Sorry, no Thomas and Margaret who immigrated abt 1886. The earliest census would have been 1900. Is there a chance that Thomas is 'Morris' and William is Morri'son'?
U S Census, 1900 ED 300 Precinct 3 Pittsburgh city Ward 28, Allegheny, PA
Citing this Record "United States Census, 1900," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/MS1B-Z12
head William Morrison M 39 May 1861 SCOT/SCOT/SCOT married 10yrs immig 1886 13 yrs
wife Agnes Morrison F 31 SCOT/SCOT/SCOT 4 children 4 living immig 1879vs 28 yrs?
son Thomas Morrison M 9 ? Jun or Jan 1891 PA
dau Georgina Morrison F 6 Feb 1894 PA
son William Mcl. Morrison M 3 June 1897 PA
son Alvand L. Morrison M 3 mos Mar 1900 PA
Pennsylvania, Births and Christenings
Citing this Record "Pennsylvania, Births and Christenings, 1709-1950," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/V2N1-XML
William Mcluckie Morrison Male
Birth 26 Jun 1897 event place: Pittsburgh, Allegheny, PA
father William Morrison mother Agnes Morrison