William has some good habits.
1. He likes eating cereal with milk.
2. He offers seats to elderly people.
3. He keeps to the right in the hallway.
4. He remains quiet during the class.
But he has some bad habits.
5. He scribbles on his desks.
6. He bullies some of his classmates.
7. He slaps his classmates in their face.
8. He slaps his classmates' faces.
[Are the sentences all grammatical? I appreciate your help.]
All the sentences are grammatically correct, yes.
Nice job!