npm dependencies and peerDependencies

I don't know if I just understood correctly the dependencies and peerDependecies of the package.json In the event that dependency b was in dependency 1 and 2, each would be duplicated with the version it requires, right? In the event that dependency b was as peerDependency of 1 and 2, it would not be duplicated and each would link to the one installed in the project, right? How would it be managed in the case of incompatibilities between the dependency version b that needs 1 and the dependency version b that needs 2?