iMessages Sent to Multiple Phones

We have just purchased a new iphone 5 and two 4S all on the same Sprint account. Whenever a text is sent to Phone 'A' (iphone 5) from another iphone it also goes to Phone 'B' (iphone 4s). A text sent from Phone 'B' to Phone 'A' comes back to Phone 'B' but is not received by Phone 'A'. When Phone 'A' downloads a new app, Phone 'B' also downloads the same app. Phone 'C' (iphone 4s) is never affected by any of this. We have now turned off iMessage on both phones and the text condition has stopped. All three phones were also signed into the same itunes and icloud accounts. A is now on a different account from B and C. The issue with the apps has continued to happen since the accounts were changed and iMessage turned off. It appears we're dealing with seperate issues.

This is more than an annoyance as the teenage daughter (Phone A) was horrified to discover that her father (Phone B) is reading her texts. Admittedly the father is also a bit traumatized for the experience. Any suggestions on what we're doing wrong?