Hi Sue,
The official number of this grave is 30 PI South.
Follow this link and it will open on a map of the cemetery.
http://www.igp-web.com/igparchives/ire/dublin/photos/tombstones/deansgrange_plan.jpgThe South Section is on the bottom left hand side. Enter the cemetery through the office gate. Take the first left and then the second right. Where the pathway begins to dogleg to the right the grave is 4 rows back and three graves in. The grave has a granite surround and appears to be well maintained. I took a number of photos but none showing the inscription as clearly as does the one posted by Joyce. This one just gives a broader view of the area.

Your relatives share the immediate area with victims of the Kingstown Lifeboat Disaster Christmas Eve 1895 and the sinking of the Leinster 1918.
Another grave nearby is that of Mary Edith Coleman who was awarded the Iron Cross by Emperor William II for her care of the wounded from both sides during the Franco Prussian War of 1870