Apple offers 2 connection methods, one of which is already available in iOS 13 beta 4.
First (not yet available): just bring two devices with iOS 13 to each other. An interface will appear for pairing two pairs of headphones. The volume on them will be regulated separately for each user.
Second: enter other people’s headphones into pairing mode and connect to them through the Settings – Bluetooth menu. In Apple Music or any other player, select two connected accessories as the sound source. [9to5]