I agree with the other posters. Did Savage's suggestion is right on the money - Asian culture venerates the older generations, so if you say you wish to honour your parents with the better seats that will be completely understood (and you will earn some respect yourself!)

You could try to do this at check-in so your parents can enjoy the lounge as well (although of course you could just give them your lounge invitations instead). But then if you tell the crew on board, they might in return honour your noble sacrifice with some better treatment (NOT guaranteed!)

Either way, kudos to you for what you are doing for your parents :-)