Azure Service Bus Sessions - possible starvation

I have a background processor that listens to a service bus queue and messages need to be processed in order per Session ID.

I'd like to ensure that no more than 5 messages are processed in parallel - meaning I'd like to process 5 sessions at once.

If there are more than 5 sessions at any given time, is there any way I can ensure that all sessions are eventually handled?

Even if I drop a certain session and then accept a new session after that, the same session might be processed again.  Can I ensure that the accepted session is the one that contains the oldest unprocessed message?