what happened to the twins in the witch

In the movie "The Witch," the twins are Mercy and Jonas, two English children living in colonial America with their parents). It is uncertain what happened to them in the movie, but it is assumed that they were taken by the witch or witches. In the end, there is a big bonfire in the woods surrounded by the other witches, who, along with Thomasin, begin to fly. It is believed that witches were able to fly using the boiled fat of a child, and it is assumed that the twins were sacrificed and their fat was used for this purpose.