So I figured out that my iPhone Bluetooth setting wasn't allowing notifications to be shown. Turned that option on, and I get text messages over Bluetooth now. I haven't yet been able to make group text messages work. I will say the MTC text message notifications box is primitive looking, and quite honestly a bit depressing, compared to the rest of the system. When I plug my phone in with the cable and use carplay, I do receive and can respond to the group messages I'm getting through the carplay interface.