Hello GMC,
I was very excited to find your message as I would love to be able to find out more about the later life of Ewen Clark Mackintosh and any descendants he has in Mexico.
I am the one with the family tree. Do you have access to the site
www.ancestry.co.uk? It is listed on there as 'The Mackintosh Family of Totteridge Lodge, Hertfordshire' (which was the home of Ewen's brother James) and is fully-referenced. As you have probably gathered from this thread, Ewen Clark Mackintosh was the son of Ewen Mackintosh, who owned Mackintosh & Co. Saddle Company. This was passed to him by his father, Alexander Mackintosh. The family lived in Haymarket in Westminster, London and, prior to that, in Golden Square, Soho, London. They are believed to have originated from Inverness in Scotland.
Ewen Clark's brother Henry Alexander Mackintosh also emigrated to Mexico, as did their nephew William Lyster Hay Mackintosh. I'm afraid I don't know a great deal beyond the details of births, marriages and deaths but am happy to help as much as I can.
Best wishes,
Miranda