If they have children who do not pray, then it is incumbent upon them to compel them to pray, either by speaking to them and ordering them, or by beating them, according to the words of the Prophet (sallallaahu Ďalaihi-wasallam)
''And beat them if they do not do it by the age of ten .'' 
If beating does not benefit them, then their case must be referred to the responsible authorities in the government, may Allah grant them success, in order to force them to do it, and it is not lawful to remain silent regarding them. Because doing so entails endorsing sin, since abandoning prayer is kufr which removes the perpetrator from the fold of Islam, so the one who abandons the prayer is a disbeliever who will dwell eternally in the Fire. If he died thus, it is not permissible to wash his body, nor to pray over him, nor to bury him in the graveyards of the muslims. We ask Allah to save us from that.
 Reported by Imam Ahmed 2:187 , by Abu Dawud in the Book of Prayer, in the chapter: When Should a Boy be Ordered to Pray? 9495,496) and this hadith is in the book sahih Al-Jamií (5868)