Derbyhaven is the bay (+ small port) just to the north of Castletown.
There were several factories in Malew - the main one was the cotton mill in Ballasalla see www.manxnotebook.com/history/ind_arch/cotton.htm but the Schofields were a long established Castletown family so possibly refered to a joinery factory ?

Jinks I don't recognise - Jick (or Gick) is however a common family name