Patty Brown has replied
with the following answer:
Valentine is likely William Dobson Valentine, James Valentine's oldest
his father's business in 1863 after apprenticing as a landscape
photographer with Francis Frith.
Not sure who
the other James (of Edinburgh) might be.
Valentine also had a son named James Morrison Hennay Valentine (b.1846)
but I haven't found any record of this James going into the family
William Dobson Valentine & George Dobson Valentine took over their
father's biz when he died in 1879."
[Many thanks to Patty Brown of Toronto Postcard Club,
Canada for supplying the above information.]