Hi Jean

You may be right , they may be cousins, hoping that with William as father they are brothers , but with so many William Callister/Collisters they may only be cousins. The adoptive theory is possible.
Strange that both Robert and Alfred's ch/birth are missing, both born Ramsey circa 1871, both with father William, that is why I am suspecting they may be the same person.
I could not find any of the Collisters from the 1871 census , with the exception of maybe James, he may be in Braddan aged 16 , b Lonan as a "Farm Servant in-door" with the Cowin family.
The name Alfred seems very rare on the IOM prior to 1900, so you would think he would be easy to find.
There is no obvious death at any time on the IOM of William and Jane , a Robert was buried Feb 1872 in Lonan aged 1 yr and 5 mths , but it was not him.
James Edward named only son Alfred and Alfred named only son Alfred Edward. No sign of the obvious William.