You can sign in to multiple Google Accounts in the Hangouts app, but you can only access one account at a time.
Tap the Home Button > the Google folder > Hangouts .
Tap the Menu icon , then tap your account.
Tap Add account, then tap the account you want to use.
Repeat steps 2-3 to sign in additional accounts.
Tap the Menu icon , then tap your account.
Tap the account you want to switch to.