I have a figure of a train car.  I also have child-figures of individual compartments in it.  You can load high-poly or low-poly rooms to the main car figure.  Each room is set up so you can open the windows and door. 

I want to write ERC code for the main train car so that you can load the main car, load the compartments, and then selecting the BODY of the main car, control all doors and windows in compartments. 

Can anyone point me to example code or forum discussions of this?