How do I use Power of Attorney to submit a tax return for my incapacitated father?

A Power of Attorney gives me authority to “prepare and sign tax returns” for my father. 

The IRS says that, as my father’s POA agent, I can submit a tax return if he's “unable to sign the return due to . . . disease or injury.”

But I’m confused about exactly how to use TurboTax for this.

I searched for the answer on Google and on the TurboTax site.

I found 3 completely different answers which contradict each other.

(1)  For a return submitted by e-file, some people say that if the POA gives you authority to “prepare & sign” a person’s tax returns, and the person has given you his TurboTax password and Signature PIN, you can submit the return by e-file with no additional steps. Some people say they have done this for years with no problem. 

(2)  For a return submitted on paper, some people say that you can sign the return like this:  Sam Smith by Jane Doe POA. If IRS wants a copy of the POA, they will ask for it. Some people say they have done this for years and IRS has never asked for the POA.

(3)  Some people say that to be completely correct and “official,” if you e-file a return for someone else, you must mail a paper copy of forms 2848 and 8453 to the IRS. Form 2848 is the IRS’s own version of a POA. Form 8453 is needed whenever mailing a paper document related to an e-filed return.

Of course, I would prefer to use Method (1).  Is that OK to use, or is it illegal? 

Is Method (2) OK to use?

Or is method (3) the only legal way to do it?