There are a few trees on Ancestry with William on , born 1878 , saying father is Thomas and mother Mary Need, whose father is given as William Need ) and pictures of Lower Tower St, and Fillongley Industrial School, where a note has been put saying William went there when he was 13 . Thomas Sheen dies in 1887( Free BMD given as source ) and Mary remarries in 1888 to a Joseph Daniels .
Maybe William born c1878 didn't get on with stepdad, and so put Grandfathers name on marriage cert ? The trees also state William marrying Elizabeth Saunders, and have William E Sheen as their son