Enabling Siri to respond to other voices on iPhone

you can't siri and multiple voices is a thing with appletv and homepods on other devices siri is mean to communicate with only 1 user

likely because that siri on the personal devices has more features, making it more difficult to decipher between a wide range of voices, and it being personal devices security becomes an issue and responding to many people could be a problem.

you can use their feedback to suggest they alter this to suit your wishes

Product Feedback - Apple