This usually happens with the iCloud account that is signed on both phones. That means, if iMessage and FaceTime is activated on both iPhones with same iCloud account, both of them will receive the call or text messages.
These are the ways that you can stop any one of the iPhone to stop receiving the calls or messages.
- Log out of that iCloud account on any one of the iPhones.
- Just change the way you receive the calls or text messages. To do this,
go to Settings > Messages > Send & Receive > Under 'You can be reached by iMessage at' un-check the email address on any one of the iPhones and leave the mobile number checked (if there is a SIM).
- Follow the same steps for FaceTime. That's it.