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If by "simultaneously" we don't mean "at the exact same moment", but rather "together" on a single controller unit, then yes, it can be done. Of course, the program handles one thing at a time in (rapid) succession, so it becomes more of a software design issue than a hardware limitation.
If I'm not mistaken, a DFPlayer doesn't necessarily require bidirectional communication (MP3 player using Arduino and DFPlayer mini - Electronics-Lab.com), but you would need to adapt the 5V signals sent from the Arduino to the 3.3V accepted by the DFPlayer's RX pin (a simple voltage divider using 680Ω/1200Ω resistors will do).
If you're comfortable with basic electronic assembly, you could control multiple DFPlayers without using all those pin pairs by using just 4 pins to drive an external decoder:
