"Many opinions are undutiful."
Translation:Multae sententiae sunt impiae.
"Multae" is nominative and "multas" is accusative. https://classics.osu.edu/Undergraduate-Studies/Latin-Program/Grammar/Cases/latin-case
To add to that, many verbs "take the accusative". That is, they have a doer of the action (nominative) and a receiver of the action (accusative).
"Sunt" is a form of "to be", which has a subject and a "predicate nominative". Both sides of the verb are in the nominative case.