The Family:
When you get to the posted coords, say hello to my Grandma and Grandpa WEBSTER.
Grandma ... Grace Louise Carr ... was an amazing seamstress, so well know throughout Guelph.
Grandpa ... Frank Edward Webster ... was a bookkeeper in Guelph for many years.
He and grandma were well known horticulturalists in the area, even creating a rose and naming it after them.
The puzzle:
The final coords are : N 43 33.ABC W 080 16.DEF, where;
There are four years on their headstone. Add up all the numbers individually. Call this Z.
i.e. if a date was 1958, then 1+9+5+8 = 23, do the same for all four dates then add all four numbers together.
ABC = Z x 10 - 54
There is also two names and initials on the headstone. Convert both names (ignore initials) to numbers using A=1; etc...
This will give two single digits. Call Grandpa's digit X and the Grandma's digit Y, thus creating a two digit number XY.
DEF = XY x 15 - 44.