Charles Edward Warren was John Olson's son-in-law.
To start, a search for 'warren' in HKGRO returns several entries. I only skimmed a couple of the results, but found the duration of his employment with the Public Works Department:
- He was employed as an Overseer on 15th Nov 1895. (See point 165, in the Report for 1895 Public Works)
- He "resigned on 1st May  on receiving an appointment under the Sanitary Board". (See point 44, in the Report for 1900 Public Works)
Next he appears in the Juror lists:
- 1902: Contractor, Wyndham Street
- 1904: Contractor, C.E. Warren & Co., 30 Des Voeux Rd Central
- 1905: ditto
- 1906: ditto
- 1907: Architect. &c., C.E. Warren & Co., 30 Des Voeux Rd Central
- 1908: ditto
- 1909: Contractor, &c., C.E. Warren & Co., 30 Des Voeux Rd Central
- 1910: ditto
That's as far as I've got - please add any further information about him in the comments below.