John Boyde s/o John & Isabella Howland seems to be in 1851 census. William must have been the older of the twins.

Isabella Boyde als Howland buried 27 Nov 1849 Ballaugh

1851 Ballaugh
Ballaugh, 03-28, 050, BOYDE, William, Glendoo, Head, Unmarried, 32, Propr 12 Ac & Occ, Ballaugh
Ballaugh, 03-28, 050, BOYDE, John, Glendoo, Brother, Unmarried, 32, , Ballaugh
Ballaugh, 03-28, 050, BOYDE, Ann, Glendoo, Sister, Unmarried, 37, House Serv, Ballaugh
Ballaugh, 03-28, 050, COWLE, William, Glendoo, Servant, , 16, Agr Lab, Patrick
Ballaugh, 03-28, 050, COWLE, Mary, Glendoo, , , 8, , Patrick

DJD