Just sticking with Carlos/Charles Tuckwell born 1868, there is an army record for a Charles Samuel Tuckwell born Glasgow circa 1868 who joined the Highland Light Infantry in January 1884 aged 15. He was a bugler.
He has a brother Frederick who lived at 4 Sussex Terrace, Mospil (?) Row, Dublin. Charles served in India and was discharged in February 1891 with dementia. His record is marked "Insane".
Also note that Rootsireland.ie has baptisms in Co Kildare for a Carlos Samuel Tuckwell 1868, also Frederick Tuckwell 1862, Albert Edward Tuckwell 1863. All have a father Sam/Samuel but that's as far as I can get without buying credits. Were they baptised in later life perhaps?