Hello 'DonnieMac',
Looked for their deaths on SP to get you started.
Problem with Ann but some possibles for Margaret even though ages don't seem to fit.
Mar (yes Mar) McKillop, mothers maiden surname McArthur, died 1880, age 52 in Kilmore District, Argyll County
Margaret McKillop, mothers maiden surname McArthur, died 1856, age 38 in Glasgow City.
Hope you strike it lucky with one of them.
PS Viewers should note that the initial posting has been repeated on the Talking Scot website. I mention this to help avoid possible duplication of effort.