Neither Tania nor her sisters ________.

Neither .... nor দ্বারা দুইটা Noun/Pronoun যুক্ত হলে শেষেরটা অনুযায়ী verb বসে। যেহেতু শেষের অংশে her sisters – Plural Noun আছে, তাই এখানে ‍are হবে।
আর বাক্যটি Passive ধারণা দিচ্ছে, তাই সঠিক উত্তর হবে are to be blamed.

• [Either/neither] + noun + [or/nor] + singular noun + singular verb.
- Neither the salesmen nor the marketing manager is in favor of the system.

• [Either/neither] + noun + [or/nor] + plural noun + plural verb.
- Neither John nor his friends are going to the beach today.

• Either and neither are singular if they are not used with or and nor.
- If either of you takes a vacation now, we will not be able to finish the work.