T.R.
I really like Patricia McConnell, PhD. She is an Applied Animal Behaviorist, and her books are well written, with clear intentions on how to train for different behaviors and results.
You can find her books at this website:
http://www.patriciamcconnell.com/store/Bestsellers/
She also has an online blog.
Beyond reading, I find it is important when training dogs to use positive reinforcement training. The way I instructed my husband on how to do this with our pack is to give an obey able command, such as "sit". As soon as the dog sits, praise is given, either verbal or cookie (or both sometimes).
If the dog does not obey, without giving the command again, "help" the dog to obey, such as putting them into a sit position. As soon as that is obtained, praise the dog! They will learn quickly enough what the command means.
Don't use the word "no", it has no meaning to dogs. You can give a redirecting command, such as "Fido, leave it!", which can be praised as soon as the dog does what you asked.
I just want to give a small anecdotal piece of advice: I read your previous post, which talked about humping & marking on your son & his clothing. We had a behavioral experience with a dog that only time was able to resolve.
We got her from friends, when they realized she was overwhelmed by their two small boys, and didn't want a bad situation. We thought she was awesome, but she was overwhelmed in our house of 5 other dogs. Plus, she had this annoying habit of squatting & peeing when she saw us, or we approached her!
So we gave her to my father (yes, she is the dog I referred to in my earlier answer). For 3 years, she would pee in the entranceway when we came to visit!! Apparently, she had so much adoration? respect? worship? for us, that she submitted immediately without provocation on sight. We had to walk in & ignore her until she had gone off to lay down, & then later pet her.
This was truly something that my father couldn't have trained out of her, and she was great when we weren't around. I do think having your son establish a more dominant hierarchy with your inlaws dog will help, and training for any dog is always a good thing! But do be aware, there may not be anything that your inlaws can do to improve the dogs behavior around your son when he is not there.
Hope all goes well, feel free to send a message with any specific questions. I've been breeding & training dogs for 14 years, lots of experience to draw on, & many mentors! T. =-)