William McWhinnie married Sarah McIlwrick. The only daughter I know of is Agnes Ross McIlwrick who married Thomas Knox on 30th December 1898 in Ayr. Agnes died 22nd September 1899 at 20, Victoria Street, Wallacetown, Ayr. Their only daughter was Agnes Ross McWhinnie Knox, born 10th September 1899.

An 1881 census entry which may interest you.

Dwelling: 48 George St
Census Place: St Quivox, Ayr, Scotland
Source: FHL Film 0203591 GRO Ref Volume 578 EnumDist 24 Page 4
Marr Age Sex Birthplace
William MC WHINNIE M 44 M Paisley, Renfrew, Scotland
Rel: Head
Occ: Tailor
Sarah MC WHINNIE M 43 F Ayr, Ayr, Scotland
Rel: Wife
Occ: Tailors Wife
Hugh MC WHINNIE U 18 M Paisley, Renfrew, Scotland
Rel: Son
Occ: Tailor
David MC WHINNIE U 15 M Argyle, Argyll, Scotland
Rel: Son
Occ: Drapers Assistant
William MC WHINNIE 14 M Paisley, Renfrew, Scotland
Rel: Son
Occ: Shop Boy
Archibald MC WHINNIE 9 M Ayr, Ayr, Scotland
Rel: Son
Occ: Scholar
Agnes MC WHINNIE 7 F Ayr, Ayr, Scotland
Rel: Daur
Occ: Scholar
John MC WHINNIE 5 M Ayr, Ayr, Scotland
Rel: Son