Power windows

My Cabriolet 1992, has Pawer windows and you can open/close only one window at a time. if you try to do it simultaneously, only one window will work.
is it meant to be like that? or its a problem?
whare the control unit located?
What can i do?

a lot of qustions……….

thanks alot!!

yep this is normal. same issue exists on corrado and early passat, its because most of the switch wires are inline with each other to make it less complicated