SInce the marriage took place before the start of civil registration unfortunately there's very little detail recorded in the register, so no mention of their fathers included in the marriage record in St. Mary's Church of Ireland Dublin CIty and no addresses or occupation, but there is a possible clue in the name of one of the witnesses - a William Hardy... maybe a brother or other relative to Sarah ?
Monkstown and St. Mary's are the parishes where the bride & groom lived at the time of marriage, but might not be where they were born. The Church of Ireland parish of Monkstown covered the town of the same name and also the town of Kingstown (later Dún Laoghaire), and also the towns of Glasthule, Bullock, Glenageary, part of Blackrock etc..
The register gives more detailed addresses for the witnesses which might provide clues - 41 Phibsboro Rd. for Wm. Hardy and 4 Kildare[?] St. for Robert Dyfen.
The best place for parish records for Dublin city is the free IrishGenealogy website, which has most of the available Church of Ireland records for the city parishes. The website also includes records for some Church of Ireland parishes in Co. Dublin, transcripts for a number of additional Co. Dublin parishes are included on RootsIreland (pay-website). There's no sign that I can see of a baptism for Henry in the Dublin City records on IrishGenealogy, as far as I know records for Monkstown Church of Ireland parish are not available online at the moment.
Pettigrew & Oulton's Directory 1847 and Thom's 1848, 1852, 1858 Directories show Mr. Henry Stevenson at 107 Upr. Dorset Street - no occupation or other details. Pettigrew & Oulton's 1845 directory shows a Catherine Hodgens, milliner and dressmaker at 107 Upr. Dorset St. The 1877 listing shows 107 as Mrs. Stevenson, and there's a possible match for Henry's death on the civil BMD index the previous year age 64. The image of this record in not available on IrishGenealogy at present but should be added soon.. Henry's Probate Calendar entry is on the National Archives website, and shows executor of the administration as a William Stevenson, son of the deceased living in Booterstown Co. Dublin, which is close to Monkstown parish.
A possible clue in the 1868 listing for 107 - principle occupants are shown as Henry Stevenson esq. & Jacob Hardy esq. ... another possible relation to Sarah ?
The children's baptisms are on the IrishGenealogy website - all St. Mary's Church of Ireland Dublin City residence 107 Upr. Dorset St. :
John Hardy 1861
Margaret Emma 1863
Annie Francis 1867
Frederick Joseph 1873
Kathleen Amelia 1878
William Francis 1878
bit of a gap between the marriage in 1842 and John in 1861 - wonder if there could have been additional children ?