What is the ruling of Islamic law on dealing with the Sabians regarding food, drink, and dwelling, and is it true that things they touch are forbidden due to their impurity?

The impurity of the polytheists is spiritual, not physical. Therefore, nothing becomes forbidden or impure by their touch. It is permissible to interact with them within the bounds allowed by Islamic law, but their prohibited loyalty (muwalat) is not permissible. It is not permissible to eat from their slaughtered animals because they are not People of the Book.