Bad word that will curse a family
If it was Cantonese, it would obviously be 冚家剷 (entire family die)

Since it was Mandarin,  the only common phrases that curse someone's entire family I can think of are:


絕子絕孫 (no male descendants, the family line ends) 
男盜女娼 (one's male descendants will be thieves and female descendants will be prostitutes)


Or it can be any cursing phrase with '你全家' before it. For example "你全家不得好死" (all of your family members will die a horrible death)