Quick follow-up. I followed @dmertz 's advice. For the code 4 1099-R, after answering it was inherited but money was NOT put into Mom's account, TurboTax then sensibly asked if it was for an RMD for Dad, to which I answered yes.
The resulting 1040 is now properly taxing both distributions, and ROLLOVER no longer appears.
I'm guessing this is the right behavior for this situation, so I'll be going with this solution unless anyone has concerns.
Thanks again everyone!
