Yes, Amy and Andrew will know to only reach out to an assistant on the meeting as long as their role is clearly stated.
The best way to have them work with a human assistant is to cue them in on your initial email while also including all of the participants, both your point of contact and their assistant. For example, you can send an email to Amy, Julie, and Sam, and let Amy know that Sam is Julie’s assistant e.g.
"Amy, please work with Julie's assistant, Sam, to schedule a call for next week."
“Amy, please find some time for us early next week. Work with Sam, Julie’s assistant.”
“Amy, let’s set up a call later this week. Please coordinate with Julie’s assistant, Sam, to confirm”
This way Amy knows to only reach out to Sam to confirm the time but still has Julie’s email address so she can send an invite to everyone who's included! This also allows Amy to send a more accurate invite and include that Sam is Julie’s assistant when listing the meeting participants.
Amy will also remember this relationship in future meetings where both people are included. If you are meeting with Julie again and Sam is added to the conversation, Amy will know they are Julie’s assistant.