Hello Danny,
The big problem is how to prove catigorically that Mary Erskine, your great grandfathers mother is also Bridget Erskine.
If Bridget, is Mary, then Bridget, died in 1902. in Largs, Ayr, aged 58 years, which is about four years out going by the 1881 census i provided, again not unusual, her death index is this spelling Bridget Friel Erskin.
On James and Elizabeths marriage certificate 1899. it states Mary Freill Erskine, is still alive, so thats another pointer.
On the same marriage certificate it states James, father is deceased, 1899. If you go by that then there is only one death for a John Friel, in Largs, Ayr. that is in 1883. age 36 years, again this is out by about 3 years going by the 1881 census i provided.
These deaths can be purchased at Scotlandspeople, for a reasonable fee, and should provide the parents names of both Bridget, and John, provided the person who registered their death had that information.
Also if you agree that the family i posted in the 1881 census for Largs, Ayr. is your family then the three birth of Michael, Maggie, and James, should provide the date of marriage of their parents which should be somewhere in Ireland.
Its really up to you whether you take the chance to purchase the certificates.
Regards,
Jonn.