Have looked all over the place - I think that William 1874 may well be the son of Juliana as he has his grandmother's and mother's maiden names as his surname.
Why is Juliana' middle name Sherman? Wonder if that is her real father's surname? But was Sarah a widow when she married William senior? I cannot find Juliana on any record at all, only on the familysearch.org (LDS) site which confirms her baptism as 23rd March 1845 and gives her name as Juliana Sherman Payne and her mother listed as Sarah Payne. Cannot find her at all - had wondered if she had died and if William was her son then he would be perhaps brought up by his grandparents? Really is a poser - but where has Juliana gone......!
I think the Williams are the same person in the different censuses.