George W. Risien was my gt-gt-grandfather and I have quite a bit of information about him plus a photo of him with his family (I think, this has yet to be confirmed). He retired to Southsea and died there in 1903.
I'm not sure how long GW lived at Cathcart Hill: I have a copy of a Power of Attorney dated 29 Jan 1891 which gives his address as 8 Cathcart Hill, but they had moved to Southsea by 1901, and his own will, dated 7 Aug 1884, states his address as 17 Maitland Park Villas, Haverstock Hill. So that would give a window of up to 17 years living at Cathcart Hill.
GW was a sugar-plantation engineer, and in the London Gazette of 11 Dec 1874 he was granted a patent for an improved method of extracting and crystallising sugar. He may sound like a fine upstanding citizen, but had his faults: in 1854 he was named as the father of his cousin's baby, which may be why he was sent out to Guiana. But he might then have had a clandestine family there before returning to England to marry in 1864 - there are "brown" Risiens in New York originating from British Guiana who claim to be descended from a "white sea captain", and GW's father captained a merchant ship.
I would love to have a photo of 8 Cathcart Hill for my records! And I will ask the owner of the family photo whether he minds me sending you a copy.
Sale, Victoria, Australia