I may try and contact someone connected with the Dungannon Cemetery to help in locating the two gravestones.
Surnames of the other daughters: Rachel born in 1834 married at Philips; Mary Ann born in 1837 married a Johnston. One other possible daughter is Margaret born in 1832 married a Bailie. This daughter and husband are shown on the other side of the Taylor red granite monument. The first Canadian Census 1851 does show the other daughters but not Margaret. Suspect she was married by then as her first child was born in 1852. Only one son was born of John and Elizabeth Taylor, my line James born in about 1830. Another note on this James was born in Ireland as was Margaret. The other two daughters were born in Canada which leads me to believe they emigrated from Ireland around 1833. Someone on one of these threads said they live on the old Taylor farm in Wawanosh.