discuss - to talk about a subject to someone.
This is usually done in a calm manner.
e.g. the teacher discussed with the parent about the child’s exam results.
debate - usually it is about a serious topic and one side puts forward their views and the other theirs.
e.g. the two political parties debated the topic of banning smoking.
dispute - an argument or disagreement about something.
e.g. the neighbours had a dispute about who the land belonged to.