Marriage is registered Sep qtr 1920. It was a Civil marriage, so unfortunately won`t be in Parish Registers, you will have to pay for the certificate.

Could Alice have been a widow , MMN Hughes and married a Evans

Deaths, could Donald have moved away after Alice died.
Alice McTavish born c 1887 died 1971 Welshpool Montgomeryshire
Donald William McTavish born c 1888 died 1974 Barnsley Yorkshire West Riding,
There is this record for 1901, the age matches ,
but you will have to get the marriage certificate of Donald
to confirm his fathers name and occupation. This will also show if Alice was indeed a widow.
1901
RG13; Piece: 3441; Folio: 113; Page: 12. All children born Livepool.
11 Siddely St, Toxteth Park, Liverpool
John McTavish 48 Police constable, b Scotland
Catherine McTavish 43 wife b I(sle) of Man
Marion T McTavish 15 dau
Donald W McTavish son 12 b c 1889Florence M McTavish 10 dau
John H McTavish 8 son
Elizabeth G McTavish 5 dau
Archibald McTavish 3 son