This sentence is not grammatically correct. It should be: Here are three more sentences that we could say are in some sense "unclear," which is to say, sentences that make us feel we have to work harder than we think we ought to (or want to). Note that it should be "make" and not "makes" since "sentences" is plural and not singular. "Here are" is not the main verb. The main verb is "are" from "to be". "Here" is an adverb of place which you say to indicate where something is physically located or to indicate that the things which follow demonstrate what you are talking about. This sentence is quite long and could be rewritten as any of these: 1. Here are three more sentences that we could say are in some sense "unclear". That is, these sentences make us feel like we have to work harder than we think we ought to (or want to). 2. Here are three more sentences that we could say are sort of "unclear". That is, these sentences seem like we have to work harder to understand them. 3. The following three sentences are sort of "unclear". That is, these sentences seem harder for us to understand. I think sentence #3 gets right to the point without using words which really only serve as filler words.

Sorry, I didn't see your comments until now. Anyhow, Mojave's explanation is great and as he says, the second "are" refers back to "three more sentences". :) Anyhow, here is even another sentence which follows the pattern of your original sentence too: Here is a book that we could say is really hard to read. This sentence could be rewritten as two: Here is a book. We could say that it is really heard to read. So when you combine the two sentences, it becomes: "Here is a book that we could say is really hard to read." The verb in the second part is "is" instead of "are" because it belongs to / refers back to "book" which is singular. It isn't referring to "we". :)

Shawn gave a great answer. But I will try to explain the extra "are" as you asked in the comment. If you take just the first part: Here are three more sentences that we could say are in some sense "unclear". You can rewrite that as two sentences: Here are three more sentences. We could say these three sentences are in some sense "unclear". The word "that" helps link the two sentences into one sentence. Here are some shorter examples: Here is a book. This book is big. Here is a book that is big. Here is a book. This book has 300 pages. Here is a book that has three hundred pages. So you can see the word "that" ties two sentences together in this example. That is why there are two "are"s in the original sentence. I hope that helps.

皆様、ありがとうございました。　中高生用の教科書を見なおしてみたら、ちゃんと「連鎖関係詞」という名称で解説がありました。　なぜか、ずーと見落としていたようです。

here are