Their opinions on the matter were different from each other's.
unlike
Frequency:
70
%
Their tastes were unlike each other's.
dissimilar
Frequency:
60
%
Their personalities were dissimilar despite being siblings.
Idiomatic Expressions for unresembling
Phrase: apples and oranges
Meaning: comparing two things that are completely different and cannot be compared
Usage: Comparing the two movies is like comparing apples and oranges, they are completely unresembling.