How can I play my alarm or phone call ringtone through Bluetooth speaker?

I have 3 teens who never hear their phone when they are at the house. Here is what I would like to happen...as we arrive home, each phone connects via Bluetooth adapter to a mixer (the Logitech adapter is great for this - it’s priced right & is very “dominant” - meaning, once you have connected to the adapter once, it consistently reconnects when the device is within range.) This mixer connects to a home speaker system.

Whenever any of us receives a call, I want to hear the phone call ring through to the home speaker system. I am using a mixer and multiple Bluetooth adapters since most adapters can only connect to a single device at a time.

My problem is that since iOS 11 (I believe?) alarms & phone calls no longer ring through to most Bluetooth adapters. Instead, only the phone’s internal speaker rings. When the same phone is connected via Bluetooth to my wireless headphones (Beats) the call is announced & rings through...just not when it is connected via Bluetooth adapter to mixer/speaker system.

Does anyone have any ideas on how I can make a phone call ring through to a speaker that is connected via Bluetooth adapter? Music plays through to the Bluetooth adapter fine & my phone is not on DND, or silent, the ringer is NOT set to “none” and ringer volume is turned all the way up.