Hi Michele, it might be possible through Power Automate... however, it depends on which criteria you'd use to determine each new member would be added to each mailing list... this would probably help you to define how to appropriately trigger an automated flow that could then use the "Add member to a group" option within the Office 365 Groups options, or even create a new event within the Outlook 365 options.
I hope this helps to clarify your options.