Legal Question in Civil Rights Law in Pennsylvania

Are you married to the man? If not, what is your relationship with him? Are there any custody orders? Why don't you want the children to be with their aunt (the man's sister)?

If there are no custody orders then the man and the children can see his sister. The only way to make it "legal" is for you to have sole legal and physical custody of the children and for you to have it written in the custody order that the father cannot take the children out of state to visit his sister and that his sister cannot be around the children.

But your question implies there are a whole bunch of dynamics at work here which you need to think about.

(1) what is the issue with the sister and your children? Is a drug addict? Abusive? An adherent of a religion of which you do not approve? Or you just don't like her?

(2) what is your relationship with the man? Are you married? Do you live with him? If you moved out with the children is that something you are willing to do?

(3) have you tried talking to the man to share your concerns about your children and the sister? If so, what does the man say?

I suggest that you think about these questions and if you are serious then go and have a consult with a family law attorney who practices in the county where the children live.