Here's the marriage from Londonderry Sentinel, 5 Apr.1861:
March 26, in Maghera Church, county Down, by the Rev. William Duffin, Mr. John Stewart, wine and spirit merchant, Endiburgh, to Caroline Eleanor, eldest daughter of Mr. James Newsam, Maghera.
The actual marriage certificate will list fathers and their occupations but not the names of the mothers.
British Vital Records Index (v.2) lists the fathers as William Stewart & James Newsam
Five children listed on LDS site which you probably have already.