The threat they use is an extreme and barbaric one: do as we say, or we will burn you and your father's house with fire.” That they join “you” (her person, body) with “your father's house” suggests that the latter refers not only to a building but also to persons. They threaten to burn with her all her family.
15 On the fourth day they said to Samson’s wife, “Entice your husband to tell us what the riddle is, lest we burn you and your father’s house with fire. Have you invited us here to impoverish us?”