Thanks for getting in touch! You can only define a single package within a single deployment step. You can configure multiple steps in your deployment process, where you can select a different package per step and scope them as needed to different machine roles. Is this what you're after?
Let me know how you go and if you have any further questions. :)
Thanks for following up! I think what you may be after is our rolling deployment feature. This allows you to define a Window size to control how many deployment targets will be deployed to at a time for each given step. Defining it to 1 would mean the step would run on all of the target servers, but only one at a time. Check out our docs for some more info on rolling deployments. :) https://octopus.com/docs/patterns/rolling-deployments
I hope this helps! Let me know if you have any further questions or concerns going forward.