Facebook Messenger Now Supports Multiple Accounts on One Device
Android: If you are using a shared phone or tablet (or just have multiple Messenger accounts), Messenger has become much easier to use. Now on Android, you can add multiple Facebook Messenger accounts.
The new feature lets you add multiple Messenger accounts to your device and easily switch between them. You don’t need to have a Facebook account to create a Messenger account. When you are signed into one account, you will only see the number of unread messages for other accounts. No one else will see any messages. You can choose whether to ask for a password every time you change your account.
Make Messenger Easier for the Whole Family | Facebook via Android Police