The CPU is similar. It's already not sleeping or in a "power sipping" mode because the game is already running. It's only going to X watts at max, it isn't like running two intense apps doubles it's TPP or something. At worse it runs two apps more laggy than one. But the power usage between one or two is probably minimal, not to say it isn't a
Go to settings then click sounds and vibration. Scroll all the way down and in the last 2 boxes u should see "separate app sounds" click on it then add what app u want to playing on speaker/bluetooth device. Once u click it everything from that app will play on ur speaker. For example I want to play YT music while watching Tiktok I can.