By default, Hypothesis reading assignments allow all students in a course to annotate together, as well as read and reply to annotations posted by all other students in the course.
If you wish to break the class up into smaller cohorts to read and annotate in separate groups there are several options available depending on your LMS and how Hypothesis has been installed.
This option requires that a Canvas administrator has installed Hypothesis using a Canvas API Developer Key.
This option requires that a Blackboard administrator has enabled a REST API integration with Hypothesis.
This option requires that a D2L administrator has enabled a Hypothesis OAuth 2.0 app integration.
These methods can be used in any LMS.