Hi
I think I have some information about your line of Frasers
I have been searching (unsuccessfully) for my GGG Grandmother Agnes Will Fraser and ended up looking at all the possible Agnes Frasers in Aberdeenshire - which led me to your family.
Isabella and Catherine's parents were Thomas Fraser and Agnes Cran who married 1 Nov 1840. Thomas was an agricultural labourer who died tragically in 1860 when the sides of a well collapsed on him. Agnes was a grocer and she is listed with her 7 children in the 1861 census in Inverurie. The informant to her death in 1911 was her son-in-law F (or T?) Betts which seems to tie in with what you already know.
Catherine and Isabella's older sister, Agnes Innes Fraser, is not my GGG Grandmother as far as I can tell. However by a bizarre coincidence, she married Robert Greig, a baker, who worked alongside my GGG Grandfather, William Murray! I did wonder if the workmates were involved with the same girl, but it doesn't quite add up. My GGG Grandparents were not married and my Agnes disappears without trace after the birth of her daughter.
I have a few records which I'll happily pass on to you. I'll PM you with details.
Cheers
Gary