I efiled my taxes. Now I need to file my deceased Dad's taxes. Can I do it on mynTT acct? Or do I need to get another edition under dad's name?

Unfortunately, with TurboTax online products, you can only file one income tax return per account.  In order to file another income tax return, you must create a separate account. 

TurboTax desktop products permit filing up to 5 income tax returns.