We have three iPhones and an iPad all assigned to one Apple ID. Anytime I try to iMessage my mum on her phone (from my iPhone), it appears on my brother's iPhone. Then, when he replies (thinking the iMessage was to him), I receive the iMessage which is addressed from my mum - despite it being sent from his phone. I've deleted the Apple ID from received iMessages to see if that would fix it, but it has failed to give the desired outcome.
How do I need to configure iMessage on the iPhones so that each person is their own "entity" and prevent "crossing wires"?