Hi Stuart,
Looks like there could be more than one family involved here. Three

Just shows the importance of getting names and dates correct - and never assuming anything.
Hope the following might help to untangle this family.
James Angus born 7 th May 1878 ??
from BDM
1878/12018 Angus James Margaret Alexander (Birth date 10 Jul 1878)
1879/14356 Angus James Jane David (Birth date
17 May 1879)
1879/14356 Angus James Jane David
William Angus 18 th Aug 1880
Parents from BDM
1880/15192 Angus William Jane David
Elizabeth A Angus 14 th Mar 1882
Parents from BDM
1882/1059 Angus Elizabeth Annie Jane David
Harry B Angus 16 th Apr 1884
Parents from BDM
1884/14040 Angus Harry Jane David
Catherine Angus 25 th Dec 1886
from BDM
1886/12939 Angus Catherine Catherine William Longman (birth 25 May 1886)
1886/829 Angus Catherine Jane David (
birth 25 Dec 1885 - but registered 1886)
As most of the children you mentioned have parents Jane and David, it looks like the Catherine born to William Longman Angus might be a red herring - and your correct Catherine has parents Jane and David

John B