Could Cuba be the point of entry into Mexico?
Easily.
A very interesting thought. It could well be.
But it would still take some bucks to get to Cuba. Who the heck is funding these people? They are supposed to be dirt poor and running for their lives.
Regular Cubana de Aviación, Aeroméxico and Copa (if you’re that brave) have flights from Havana to México City. Cubana also has flights to Cancun. Why not roll in a beach day into your terrorist plot?