To contact just your sections, create a course reflector in UMEG (I can show this to you on Friday, as well).
To contact all of the students (all Losert's and all Redish's), that can be accomplished through "Announcements" on ELMS/CANVAS--but try not to do this without first checking with the Professors (we don't want to swamp student inboxes).
You could ALSO (and this is time consuming at first, but then you can just respond to the email over and over as a continuous string), use the "Inbox" aspect of ELMS/CANVAS and individually select your students from the whole-course student pool (thus emailing only your students). The most recent version of ELMS/CANVAS also seems to allow you to select an entire section of a course (e.g., section 0203) to email from the inbox.
Perhaps this last way (or the UMEG method) is best.