By default there is no way you can login to two accounts in skype. Here is a way you can however do it via your ubuntu terminal.
Step 1: Open your ubuntu terminal.
Step 2: Type the following command on the terminal.
skype --secondary
Step 3: Now login to your other Skype account and enjoy.
Please note that do not close the terminal. Keep it open until you logout of this new Skype account.