Most likely they are actually Fn+F11 and Fn+F12 but BIOS has them reversed so you don't need to press Fn. When you press Fn+F11 and Fn+F12, what you actually get is F11/F12. If you look in your BIOS options, you will probably find an option related to this reversal. F11 and F12 have standard PS2 scan codes unrelated to the brightness keys.
Your keys are likely handled via ACPI as is the case for most modern computers. They keys are probably tied to a pair of EC query methods. Use the instructions in post #1 to determine which methods are activated by the keys.