Similarities: In both the book and the movie, Greg's character is portrayed very alike, with very few differences if any, and most of the things he says are the exact same. Rachel's mom is also a very similar character who seems to love Greg and is so thankful that he comes over to keep Rachel company. The rest of Greg's family is the same as the book, his dad being a stay at home dad who is lazy and walks in his pajamas all day long. Greg's mom is very protective and likes to be involved in Greg's everyday life.
Differences: Some differences are that in the book, Greg's sisters are mentioned multiple times, and then in the movie, they don't come up once, and we know nothing about them. Also in the book, Earls mom is described as someone who isn't involved in her child's life, and she doesn't seem to want to be. In the movie we don't see her mom once, and she isn't mentioned, so we know nothing about her.