My iPhone 5s keeps changing the the name of my contacts?

My new iPhone keeps change my dad and my friends contact name to there number and removes there picture. My phone service is Verizon. Only my dad and friends contacts are changed not my mom, cousins and businesses are not changed only dad and my friends. Is there a way to stop it from changeling the contacts names

If you are signed into icloud with the same apple id as another person they might be changing it on their device thereby changing on yours.