If on a call with AirPods, can someone else’s AirPods chime in on conversation if their AirPods have been used on my phone before ?

Hi,

Open the settings app > bluetooth > if the other persons AirPods are on the list, that means they can wear the AirPods and listen to the audio from your device.

You can tap the “i” next to the other persons AirPods and tap “Forget this device” to fully remove it.