My sister's ex is such a nuisance

Dear Harold,

I am writing on behalf of my elder sister whose marriage hit the rocks and ended up with a separation in court following perpetual physical assaults by her husband. Despite their separation, her husband does not respect her space. He unashamedly walks into her house at odd hours demanding to see their three children. During their separation, the court had set timelines on when the children can go to his place — mainly weekends. He has, of late, turned into a stalker, hounding her with advances that they move in together, which my sister is against. Is there a way my sister can stop his advances and unbecoming behaviour in contempt?