There should be no hardware limitation for how many devices could connect via Bluetooth. I suspect there is a limit of 1 of concurrent connections which is not something I would suggest changing even if it were possible. However, what I would change is the order a car automatically connects...
My daughter and her partner purchased Rivian and set their phones as keys. I am also driving the car and would like to use my phone as a key and have access to the rest of the app functionality (which is very limited compared with Tesla).
To my immense surprise, there is a limit of 2 keys. It...