How to make the sound play through my AirPods and HomePod?

you can change your audio source from your AirPods to your HomePod or vice versa. Check out the resources below to see about using control center to change your audio location.

Use and customize Control Center on iPhone - https://support.apple.com/guide/iphone/use-and-customize-control-center-iph59095ec58/ios

Switch AirPods between iPhone and other devices - https://support.apple.com/guide/iphone/switch-airpods-between-devices-iph08b253c17/ios

I don't think that is a supported arrangement. Multiple speakers or potentially multiple AirPods, but not both. Use Feedback - HomePod - Apple to share your thoughts with Apple.

tt2