Dear Federico,
FAST standalone cannot be used to model two turbines, but NREL has developed SOWFA and the soon-to-be-released FAST.Farm tool for that purpose. And UMass developed DWM. More information e.g. at: Simulating two turbines (one behind the other) - #14 by Jason.Jonkman.
That said, neither SOWFA, DWM, or FAST.Farm support an interface to Simulink.
Best regards,