I hope that the administration views this as an experiment in which proven pedagogy isn't ready for prime time. If not, you will have some difficulty. If they do, then stay flexible and modify things as you learn more.
For an online class you can do the following with a bit of help from your IT department.
Establish a private mailing list. I suggest under the control of the university, not something like Facebook (privacy, security, ...). Subscribe every student to the list when they register. Unsubscribe them a bit after the course ends for them, say, when their grade is posted.
In addition to whatever you do online with zoom or whatever, have the students ask questions on the list. Everyone sees every question. Everyone sees every answer. If you can get the entire set of list interactions preserved and visible to all students, all the better.
I've used this in other situations with groups of widely varying background/experience. It is helpful even in more normal classroom situations because those when a question is asked it is often likely that others had the question and didn't ask it. The classes I taught with this tool met infrequently (once a month), but were 24 by 7 from the student standpoint. When they had a question, they asked it and got an answer, maybe from me, or not. But their progress was never blocked.
The list is used for everything except communication that is personal (grades ...). All content questions go to the list so everyone sees every interaction.
Encourage students to answer questions posed on the list - answers back to the list. This cuts your load immensely. You only need to respond to answers that might lead to misconceptions. But make sure that the list isn't used to pass answers to exercises to other students. Minimal hints are fine, but not answers. Perhaps questions about exercises can only be answered by yourself (or a TA).
Second, as much as possible, "flip" the classroom so that the real time sessions are not content delivery. Use readings for most of the content. Look for a way to encourage the readings on a topic prior to discussion in real time. A quiz on the readings is useful for this if you have the tools for it. The quizzes count somewhat toward the grade. Taking the quiz is the ticket to participate in the real time session if you can make that work. Graded quizzes might be enough. You might need three sets of quizzes, one for each "level".
Alternative to the open mailing list, if questions come to you and you post the important questions and your answers to a list so that all can see them. Then you don't get the same question ten times. But having other students answer questions is a big time saver, though you have to read the list frequently.
I could add more for a face to face situation.
Caveat. I can't predict how the students will benefit or not from seeing material "out of order" and with things at different levels "all at once". It might work fine, or it might be a disaster. You need to monitor that and give feedback to administration on your observations.
