separate apple IDs on same email address
No - an Apple ID is a unique string, so you can't enter the same letters for two as the first reserves that "email" and prevents a second account.

You can have alases in one email account so that mails to more than one address get delivered to the same account. Google allows this with punctuation and arbitrary letters after a + in the email name. You can also enter punctuation like periods so if your email is RobynWhatever, mail to Robyn.Whatever also gets delivered to the first gmail account.

The only way is to have separate email account, you cannot use the same email for different account.

If I understand correctly, you want to have control over those accounts and receive the monthly purchased email in one account. You can setup 2 email accounts with forwarding service which will send all the mail from their account to your main email account.