These books cover everything you need to pass the grammar section. I completed the level 3 & 2 grammar books and honestly blew through the grammar section both times when taking the JLPT. I never rely on one resource for studying, but I would contribute the majority of my success to the Kanzen Master series.
The N3 grammar book contains English explanations where as the N2 book doesn’t which can be quite daunting at first but hang in there and you will do fine. There are several grammar resources you can check online to find an English Translation of a grammar point, my favorite one being renshuu.org.
In the Kanzen books you will have a 2 pages with several grammar points with often similar meanings. Each point is given an explanation in Japanese (and English in the N3 book) with 2-5 example sentences to help you grasp the meaning. The example sentences do no not have any English translations, and a few can be tough to understand at first. I recommend highlighting all the words you don’t know and adding them to your Anki vocabulary deck later. Also, highlight any sentences or grammar points you don’t understand fully so you can easily come back to them later. I was quite often surprised to find that although I couldn’t understand something at first, it would just suddenly click the 2nd to the 10th reviewing it.
On the pages following the grammar points you will be given review questions to see how well you understand. After you cover so many grammar points you are given an even bigger review quiz that helps you retain everything you learned. The style of the questions will be just like the ones on the test, ones where you have to choose the correct grammar point to be used in the middle of a reading passage and also questions where you have to put the sentence structure in order, my personal favorite.
At the end you will be given a mock exam. That’s whats great about this book, all the review questions and drills you do will burn the grammar into your brain. It’s ordered nicely so that you often have to recall previous points. You will be forced to flip back through the book in search of grammar points you can’t remember.
Now as I said before, I didn’t solely rely on these books for the exam. One other resource that I used was Anki. I make sure I do my Anki reviews at least 5 days a week. Here are the 2 grammar decks that I highly recommend that you can search for and download: Nihongo So-Matome N2 Grammar and Nihongo So-Matome N3 Grammar. As you can see those decks where made from the So-Matome series. They are not a bad series of books, just inferior to Kanzen Master, but great material to supplement with.
If your in Japan you can find this book for a cheap 1200 yen. If not you can find it on Amazon.