Father remotely reading adult sister's texts

I'm not sure if this is the correct sub, and if not, I would really appreciate someone pointing me in the right direction!

My father, who the rest of my family is pretty sure has narcissistic personality disorder, pays for my sister's (22) phone, and they are on the same plan. We have a number of reasons to believe he has been reading her text messages, which is big problematic due to dad's relationships with other family members that she …

adult father privacy