No you cannot have two controllers with different memory size in the same controller tray. It will not work and the FW will lock down at least one controller, provided that you do not encounter other unexpected problems.
This will not work because the 1GB controller and the 2GB controller have different sub-model IDs which are electronic numbers allowing the FW to determine what features are supported with the controller. You cannot modify this sub-model ID, it is modified in the manufacturing. Therefore, you can change the memory but the sub-model ID are different, hence once you insert a controller with a different sub-model ID than the one which is online, the FW will lock down the controller you inserted with a different sub-model ID and it will not be useable. Therefore, I'm afraid that what you want to do will not work.