What can I do if my teenage daughters do not want to return to their mothers because their stepdad is threatening to kill them?

You have several options. You can file a motion to modify custody based on a material change in condition that negatively impacts the minor children. If the children 14 years or older, the trial court judge should consider where they would like to live, i.e., which parent's house.  Additionally, you could file an emergency motion to modify custody where the minor children would not have to be at the stepfather's house and if said motion is proved by the judge, then the children would immediately be protected from having to be in the presence and custody likely of the mother. Also you could probably TPO, also known as a temporary protective order. I do recommend that you act quickly and obtained an attorney. Best regards, Susan D Taylor Magruder & SumnerRome, Georgia706- 291-7050