How to support models of different projects but one application?

Question

Ruby on Rails

One project, but divided into two parts. One is pure API, separated into a separate Rails API application (for mobile). The other is also a separate application (for clients).
Of course, migrations and models intersect. Book is in one project, in another.
Question: is it possible to concentrate the models in one place? If not, what is the best way to maintain or build it all? I'm afraid to get confused when something was removed in one model, but not in the other.

Answer 1

It is not clear what is the problem with using one api in both cases, and giving the rest to the client side?!