I have a question for a very specific need.

I am a sub contractor for multiple design agencies. Each one assigns me an email address with their brand / domain. I need a calendar function that allows me to have different branded calendars connected to each of my different email accounts ------- For availability I need to be able to connect to my main Google Calendar but for scheduling I need the appointment to be saved into the respective branded email Calendar.

Is that possible? Or would i just need to buy 5 separate accounts to accomplish this?