Later twins:
Margaret Keenan, mmn ONEIL, Mar qtr 1862 Haltwhistle
Mary Ann Keenan, mmn ONEIL, Mar qtr 1862 Haltwhistle
Thanks, I hadn’t found that, looks like she was Jane oneill.
The other strange thing is Margaret seems to appear with the family in the 1861 census, but obviously she can’t as she wasn’t born yet and is a twin
Update, it looks like the original Margaret was born in abt 1860 and died as an infant, the twin Margaret is Margaret the 2nd 
Is this the family 1871
James Keenan Head M 37 Ireland
Mary Keenan Wife F 36 Ireland
James Keenan Son M 13 Carlisle, Cumberland
Margaret Keenan Daughter F 9 Haltwhistle, Northumberland
Mary Annie Keenan Daughter F 9 Haltwhistle, Northumberland
Robert Keenan Son M 7 Haltwhistle, Northumberland
John Hammel Stepson M 13 Scotland
Patrick Hammel Stepson M 11 Scotland
Patrick Kerney Lodger 70
RG10; Piece: 5154; Folio: 29; Page: 51
Their marriage entry
Registration Year: 1868
Registration Quarter: Oct-Nov-Dec
Registration district: Hexham
Inferred County: Northumberland
Volume: 10b
Page: 450
Name
Hannah Green
Mary Hammell
James Keenan
Jane Turnbull
Possible first marriage for Mary
Mary Cairney
Marriage Date: 3 May 1857
Marriage Place: Annan,Dumfries,Scotland
Spouse: Isaac Hamel
Patrick Hamel
Birth Date: 5 Apr 1860
Birth Place: Annan,Dumfries,Scotland
Father: Isaac Hamel
Mother: Mary Carney
Name: Mary Carney
Spouse: Isaac Hamel
Child: John Hamel
1861c RG 9; Piece: 3866; Folio: 16; Page: 26
Isaac Harriel 30
Mary Harriel 26
John Harriel 3
Patrick Harriel 1
Patrick Carnie 58
Michael Oniell 38 lodger