Deep learning error: All layer names should be unique
The problem is, you are trying to instantiate two VGG16 models at the same time and its confusing for the kernel to figure out which graph it needs to use. Atleast that is the speculation I have, because of the problems faced when trying to load multiple models in keras with tensorflow backend, its not straight forward. 

Try commenting the code from when you are instantiating the second model and this error should go away.