Hi,
In my opinion, I would consider moving the models classes to a separate project that could be referenced by all the different modules that requires them, as Damian suggested in this previous thread (WPF PRISM modular design). This shouldn't be wrong, as Prism recommends that modules should not reference each other, but not that they shouldn't share common projects between them if required.
Regarding this topic, I believe you could also find the following threads interesting, where similar discussions have been addressed:
I hope you find this handy,
Agustin Adami
http://blogs.southworks.net/aadami