With all the info provided by everyone so far.
This looks to be the 1901 census entry for the siblings, William and sister Helen Hill, mentioned:
James H Hill 39 grain miller
Margaret E Hill 37 b. Girvan
Helen S Hill 9
Matthew H Hill 3
Rebecca Mckinlay 22
Annie M Boyd 23
Address: 25 Forsyth St Greenock
James Hamilton Hill Snr above looks to come from a family of grain merchants. See here for example
www.thegazette.co.uk/Edinburgh/issue/14365/page/963/data.pdfMargaret Hill his wife, maiden name looks to be LUSK. Likely sister to Andrew Potter Lusk given the reference to nephew and niece mentioned earlier by William from APL's will.
A great source of info is likely to be the Watt Library in Greenock and their online 'Intimations' database. From that for example is the marriage of James Hill and Margaret Earl Lusk:
Marriage: HILL James 1889 James Hamilton Hill, grain miller, to Margaret Earl, 2nd daughter of John Lusk, at Rosevale, Greenock on 12th September 1889 (Greenock Telegraph).
Monica