2-place Intercom and 4 Headsets

Hello community,

imagine you have a plane (rented) with a build in 2-place intercom
(sigtronics in this case) and want to give your passengers their own
headsets, so you can communicate with them. It is not necessary for them to
hear the radio transmissions you make, although, it would be nice (if legal
;-).

What do you need? An additional portable 2-place intercom? A Y-cable
extension?

Thanks in advance for your answers.

Regards

Kai Glaesner