It depends on what development environment was used to produce the original apps. There are a number of cross-platform environments: PhoneGap, Qt, Xamarin, probably others. Of course, even in that best-case scenario, it is not simply hitting the "Compile for Android" button, they would still need to do all the testing for the new platform.
If they used the "native" development environment, then porting them to another platform would essentially amount to a rewrite. If they used C# originally they might be able to re-use some back-end code by going to Xamarin, but the GUI would need to be rewritten.
Biting the hand that feeds IT
