Hi
Hope this is of some help..
Daniel's death reg. suggests his birth was about 1826.
Ireland, Civil Registration Deaths Index, 1864-1958:
Name: Daniel Dornan
Estimated Birth Year: abt 1826
Date of Registration: 1876
Death Age: 50
Registration district: Downpatrick
Death Country: Ireland
Volume: 1
Page: 441
FHL Film Number: 101588
Ellen b. abt. 1840:
Name: Ellen Dornan
Estimated Birth Year: abt 1840
Date of Registration: Apr-May-Jun 1905
Death Age: 65
Registration district: Downpatrick
Death Country: Ireland
Volume: 1
Page: 403
FHL Film Number: 101602
Ireland, Griffith’s Valuation, 1848-1864:
Occupier: Daniel Dornan
Lessor: Robert M'Dowell
County: Down
Barony: Dufferin
Parish: Killyleagh
Townland: Cluntagh
OS Page Numbers: 23, 24, 30, and 31
Geoff