Hi Andrea,
I don't know if this will help but what you really need is your fathers birth certificate. Was your father born in Scotland?, if so his birth certificate it would give you the names of both your grandparents (which you will already know) but it will also give the date your grandparents married and from this marriage certificate her age which would give you a better idea of when and where she was born.
With a name like Honour Stella Lamb you shouldn't have any problem finding her birth, just be glad her surname wasn't Smith!!
added later!!! Sorry I should also have said the death cetificate of Honour Stella Lamb would also give you her marriage date.
Betty