The correct option is are.
"The members of the jury are divided in their opinion."
(The subject is 'members', a plural noun, so the plural verb 'are' is used.)
The noun closest to the verb is 'jury' (singular), but the actual subject is 'members' (plural). This is a common trick in subject-verb agreement. Always identify the true subject, ignoring intervening phrases. 'Members' is plural, so it takes the plural verb 'are'.