Today my sister asked Siri on her phone what her name was and Siri said my name. So we checked the contact and she had all of mine. She deleted the ones that weren't hers. I checked on my phone and the ones she deleted were lost off mine too. I have no idea how we are connected. We have had our phones since Christmas and it's now almost June and it's been fine until now. I want to know how to fix it because it's going to get quite annoying. Nothing else seems to be connected. We aren't receive the same texts or have the same pictures or anything. Just the contacts. Also we both have the iPhone 5c if that helps.

Do you both have an email account or other Apple account that you have both logged into to and saved the same settings on both phones? In other words, the SAME account on both phones?