Your worry lies in the ownership of the house after your father's death.
Question 1: Does your stepmother and stepmother's daughter have the right to inherit after her father's death? It depends.
If your stepmother has never registered marriage with your father, they are not married. After death, it is treated as cohabitation, and the property during cohabitation is treated as * * * with the property and belongs to * * *. Each belongs to his own property, that is to say, they have no inheritance right!
Question 2: If your stepmother and your father are registered for marriage, then your stepmother, as the first heir after your father's death, has the right to inherit your father's property. As for whether your stepmother's daughter can inherit, it depends on whether she is an adult when your father marries your stepmother and whether she has formed a de facto relationship with your father, so she has the right to inherit. Has grown up, if there is no molding, there is no custody!
Question 3: Your father can make a will and inherit all your property. Testamentary succession takes precedence over legal succession. Even if your stepmother and your father get married, even if your father and your stepmother's daughter form a foster relationship. They are not allowed to share property.
If so, the best way is to notarize this will in the notary office, so that the effect of this will will be stronger!
Of course, beside the point, as a stepmother who lives with your father, I think it is more or less helpful to take care of your father, and the law does not prohibit them from enjoying the right of inheritance.
Of course, you have to persuade your father to make a will. Of course, I don't think this matter can complicate family relations!
Personal views are for reference only.