I've actually had great frustration with Apple bluetooth, but I think a higher levels of the stack.
My wife has an iPad, iPhone, Apple watch, and iPods.
I have just iPods.
There are countless times when I'm listening to the iPad with my iPods, and when she comes into range, either my iPods switch connection to her iPhone, or her iPods steal my connection to the iPad.
I've found no setting on any device that fixes this. It drives me insane.