Google Books comes up with a mention of the Coins book, but only a snippet view.
Does mention though
The name was again changed in 1863 to Dickson, Tatham & Co. Tatham was a nephew
of Duncan Dunbar, the millionaire owner of the Dunbar Line of first class...
You may already have these
The Times, Friday, Jan 08, 1847; pg. 7
On the 7th inst, at Poplar Church, William Smith, eldest son of W. S. Brown, Esq., of Brunswick-terrace, Commercial-road, to Phoebe, eldest daughter of Christopher Tatham, Esq., of Poplar, and niece of Duncan Dunbar, Esq., of Limehouse.
There are a few other death and marriage notices for children of Christopher Tatham, but not sure if they are sisters of DDT or half siblings, Robert Gordon, Elizabeth Patty, and Augusta Louisa. Robert Gordon died at 69 East India Road, Poplar on 3rd Dec 1895, aged 66. Says he was the eldest son of Christopher Tatham, Surgeon. In saying that one could assume that DDT had died by then.
Ian C
EDIT
Just found a marriage notice for Robert Gordon Tatham in the Morning Chronicle of July 6 1857, when he married Emma Dixon on 2nd July at All Saints, Poplar. That article says he was second son of Christopher Tatham.
Christophers death notice in the Morning Chronicle Apr 2 1861, saying he died on 28th March.