Solved
I've just submitted my 2016 taxes, but need to file two other separate forms for my mother (who is deceased as of April), and my brother (whom I've already claimed as a dependent on MY forms, but he has a 1099-R form of his own to file.
In TurboTax Online you cannot prepare another tax return in the same account. You have to use a separate user ID for each return. You cannot prepare another tax return with the same user ID that you used for your own return.
See the FAQ at the following link for instructions to start another tax return with a new user ID.
https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online
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