After you check the states of the buttons I think you need to check for both being pressed first before you deal with individual presses. And when you first detect both being pressed you should start a millis() timer so you can ignore the fact that both are pressed unless they stay pressed for a minimum time.
I suspect the logic of the system would be easier to think about if you focus on buttons being released when a foot is lifted rather than being pressed when a foot is put down. Pressed is the normal state. released is the unusual state.
...R