Is this stalking or harment?

when ever my bf has his kids his ex tell him she is having someone watch him.. weather it is at our house or his parents.. she has gotten so bad with the letters and phone calls i wont let the kids come over .. he has to take them to his mom house.. now in the begining in one of her letter she sugessted that she was thinking of doing this..making him go to his mom house with out me.. after so much of it i thought it a good idea.. now she is mad about it and call me a ***** on the anwswering maching.. said if he wasnt at her mom house with out his ***** old lady and that if he did not come alone he could never see the kids again.. they were never married so she has 100% control of the kids.. is this stalking or harrsament.. he did not go and a month and half later she called for him to get the kids.. he took them to his mom house after her asking and him telling her 6 times where they would be at... and her calling and her parents and grandparents calling the entire week end to make sur