Correct, they are only in Trinidad South
Not sure what you mean by bus "strategy". There is a bus stop for every "village" and Old Port Royale. The order of the stops is determined by where the bus enters the property. There are 2 entrances the bus can come in. Even if you're the first stop on the loop for pick up, your friends will be exiting the property to your park of choice in less than 8 minutes per our last trip.
If they use the Disney Magical Express, after check-in there is an internal resort bus that will take them from the Custom House to their village. About 2 hours after your arrival, Bell Services will deliver their luggage to your room. There is no luggage allowed on the internal bus. Upon check-out, they can call bell services and they will come pick up them and their luggage and take them to the Custom House.