This is a bit of an odd question and I’m not sure I understand what is being asked. Most grand pianos have 88 keys, spanning 7 and 1/3 octaves. Keyboards with 76 keys are available for purchase and these span about 6 1/3 octaves.
Therefore, there would be no reason to have to play two keyboards, as long as you’re playing one with 88 keys. If you’re playing on a keyboard with 76 keys, chances are you won’t miss the bass and treble octaves because they are located at the far left and far right of the piano.