Photos on old iphone being transferred to new iphone
Welcome to Ask Different. It sounds like you two are using the same iCloud account. Go to Settings -> iCloud and look at the email address listed at the top. If you are both signed in to the same account, you will see each others' photos. This also poses a problem for iMessage. If you two are using the same account, one of you needs to create a separate iCloud account, sign out on one device, and sign in with the new account.