Whether you need to take permission once again depends on how you are using the interviews in the book. If you are including information about the interviews that is already mentioned in the published article, I think it should be fine to just cite the article as the source. You need not take permission from the interviewees once again in that case. However, you should be careful to phrase the text appropriately so that it is clear that your source of information about the interviews is the article.
On the other hand, if you are using any information from the interviews which is not included within the published article, you have to take permission from the interviewees once again.
However, conventions may vary across fields; therefore, it might be a good idea to check with your supervisor or a senior colleague before you submit your book for publication.