For the photographer, you need a contract either assigning you the copyright (perhaps as work-for-hire) or licensing the images from them. Be sure that the person operating your camera knows how to use it! A publisher's photographic standards are likely to be high.
For the people in the photographs, you will need a model release. It would be a good idea to get one from the owner of the dog/s, too.
Unfortunately, I don't have either on hand, but googling should bring up plenty of sample contracts and release forms that you can tailor to your specific needs. (And your specific location. Be sure you get one that is appropriate to your country.) There are also books with sample legal forms for photographers. Caroline Wright (of Photoattorney.com) has written one, and there's another by Tad Crawford. If you look at Crawford's, which has been around for a while, be sure it's a recent edition.
Meanwhile, though, someone else here at AW might be able to offer something.
Good luck with your book!