Two phones linked
My FaceTime calls are going to my personal and my work phone even though they have separate Apple IDs
Question marked as
2 options, either, they are using the same Apple ID, at least for FaceTime or you may have call forwarding turned on.
On both iPhones go to Settings->FaceTime->Apple ID, and make sure they are logged to different Apple IDs.
Then go to Settings->Phone->Call Forwarding, and make sure your other phone is not added there.