Did we have Sir Archibald Orr Ewing remarrying?? I've come across a webpage that says he married a Mabel Addington in Oct, 1879
http://www.pellew.com/Family%20Tree/Family%20Tree.htm
I think this is the marriage recorded on Free BMD for Dec 1879 that you mentioned earlier - there were 2 husbands and only one wife, so Mabel wasn't actually listed.
Here they are on the 1881 census:
South Cliff, Holdenhurst, Hampshire
Archibald E O Ewing Head 28 (??)Late b. Lanarkshire, Scotland
Mabel Ewing Wife 22 b. Devon
Norman A Ewing 5m (or 5wks?) b. Argyll
(Plus 2 servants.)
RG11/1195 - Folio 61 - pg 60
And in 1891:
Park View House, W Chester Rd, Towcester
A E Orr Ewing Head 38 East India Merchant b. Glasgow, Lanarkshire
Mabel Ewing Wife 37 b. Up Otley, Honiton, Devon
Norman A Ewing Son 10 b. Argyllshire, Scotland
Violet E Ewing Dau 9 b. Dumbartonshire, Scotland
Earnest P Ewing Son 8 b. Ayrshire, Scotland
Mabel U Ewing Dau 3 b. Perthshire, Scotland
Alice M Addington Sis-in-law 41 b. Up Otley, Honiton, Devon
(Not to mention a governess and 9 servants - business was obviously doing well!)
RG12/1188 - Folio 138 - Pg 15
Rambler