It is only possible to log into one account at a time using the MetaTrader 5 app. However, you are able to switch between your accounts. To switch between accounts:

• Go to Settings and the top item should show your current account.
• Touch your current active account and a new screen will appear showing your other available accounts.
• Select your desired account to log in or select the ‘+’ symbol at the top right to add a new account.
• MT5 will now be logged in with that trading account.