William Killip who married Catherine Cowle was a brother of Heber. They both appear on the 1851 census - William at home & Heber on a neighbouring farm. There is no evidence that I know of that William was ever called William Heber.
On the other hand, I can find no baptism for William & I can't find the family on the 1841 census, which should settle the matter as they should both be at home at that time.
The family then should have been
James
Ann
James
John
Heber
William