Remote trigger shutter on two smartphones at once

I have a working stereo rig that uses two smartphones (Google Pixel 3A). I need to be able to take long exposures, so I need to remove the risk of shake from manual contact with the phone, so the final hurdle I need to overcome is triggering both cameras at the exact same time remotely.

There are various remotes (like this one, but they all appear to have the limitation that they can only connect to a single phone at one time (this is a Bluetooth limitation I believe). My current solution is to buy two and attach them to each other, but this isn’t ideal.

Does anyone know of a way to trigger two smartphone cameras at the same time remotely.