Complex sentence: Ali and the mullah need one more "witness" to Soraya's "infidelity" to be able to formally charge her, so they visit the widower at home and using threats manipulate the widower into agreeing to back up their story.
Split into simpler sentences: Ali and the mullah need one more "witness" to Soraya's "infidelity" to be able to formally charge her. They visit the widower at home and, using threats, manipulate the widower into agreeing to back up their story.