Yes, you can send campaigns from multiple email accounts simultaneously.
To send emails from multiple email accounts simultaneously, you have to pay for each email account. So, if you want send campaigns, from 2 different email accounts at the same time, you need to subscribe to 2 Sending email accounts.
To add more email accounts to your subscription, go to
Settings -> Billing -> Update -> change Number of sending email accounts -> Update
You can send multiple campaigns from the same email account, or
you can reuse the licence by pausing campaigns from one email account and sending newer campaigns from another email account..