you can try and set correct permissions for the additional accounts and then have them accessible through the “additional mailboxes” feature; another thing you may try is to setup delegation for the mailboxes.
I hope this helps.
To save effort and maximise on ease of use, I would change the account setup to include each of the alias addresses as it’s own IMAP/POP3 account – this way also all mail will be stored in the sent folders. I know it’s not perfect, but if you want to be able to send from the correct multiple addresses, it’s all I can think. You could still have them all returning to a central shared exchange account, and just use IMAP for transmission?