Hi bjaxed – congratulations on finding Rootschat, you won’t be disappointed in doing so!
CD Gordon Snr had a son called Thomas Gordon (born about 1850, died late 1890s) he migrated over to Liverpool and then settled in Manchester. He married an Amelia Croston. I did quite a bit of research on this couple for a friend, they are his great grandparents.
CD Snr also had a daughter, Fanny, who married J C Baird. Her existence was found when searching the newspapers on the British Library site. It was an announcement about her death which confirmed that she was the daughter of CD Gordon, a Professor of Music. She died in 1888.
I found another announcement about one of his children. Charles D Gordon jun, “third son of Mr Chas D Gordon, teacher of music, 9 York Street Belfast”. He died in 1872.
I believe I have managed to track down information about CD Gordon’s Snr birth/parents. Charles Duncan Gordon born 04 September 1829 at Kelton, Dumfries. I then found this about a brother: 13 July 1837 - James Kirkpatrick Macdiarmid Gordon father James Gordon, Teacher of Dancing mother Fanny Hall, Dumfries. (I also found a reference to Fanny's death in Belfast.)
Hope this helps you to make a connection or rule one out.
Good luck with your research
Pip