1) The Twins would overpay for Realmuto. Forget it.
2) Why the heck would the Marlins give up a good, cheap guy they can control until 2021? They can build up the rest of the team without giving up their once-in-a-generation catcher. Every other position will prove much easier to upgrade.
Which position is easier? They're not giving up on one of these out fielders. Or SS, assuming they like Polanco. Or 2b, unless they upgrade from Dozier? Or third base. And not first base this year.