The Purdue University Copyright Office website has a great deal of content regarding fair use in classrooms: https://www.lib.purdue.edu/uco/
See this page for basic copyright information regarding transforming your in-person classes to online.
See this page for details regarding the four factors of fair use, and the very top of that page for the four-factor fair use weighted analysis.
Contact the Director of the University Copyright Office, Professor Donna Ferullo, if you have questions that cannot be answered by the Univ. Copyright Office website: https://www.lib.purdue.edu/uco/