Looked up Margaret Coutts death on Scotlands People - she died aged 76 on 3/9/1862, married to Alexander Coutts, Crofter who was the informant of her death - cause of death not given but her parents are given as:
James Simpson, Farmer (deceased) and Margaret Simpson, formerly Williams (deceased).
The place name given on the 1851 Census transcript as Keldrammie should be, I believe, Kildrummy which is just up the road from Towie. The parish births for Kildrummy are on IGI but the only Simpson ones there are:
Peter bp.6/4/1770, James bp.1/1/1762, George bp.19/10/1766 - entered as Symson and father of all 3 being a James.
Simpson baptisms at Towie are all children of previously mentioned John Simpson and Isobel Dickison (or Duckison):
Adam 7/7/1827, Alexander 4/1/1815, Barbra 5/7/1823, Isobel 4/1/1811, James 3/6/1809, Jane 16/11/1817, John 2/2/1813, William 26/3/1819 - alas, Arthur's not shown.
Only other one at Towie is Margaret 6/3/1837, dau. James Simpson and Margaret Milne and this could possibly be the Margaret - gt. niece - with Alexander and Margaret Coutts in 1851 (even though birthplace then is given as Kildrummy).
In Scotland the eldest son is usually named after paternal grandfather - as John and Isobel named theirs James this would tie in with the parents given for Margaret Coutts.
That's as much as I can find on-line I'm afraid.
Good Luck.
Annette