What is the religious ruling regarding the intentional defilement of multiple places – such as a car, a house, and a hospital – by sitting on them while impure? And is it obligatory to inform their owners about this and to purify these places?

If you intentionally neglect to purify yourself from impurity for the sake of prayer, then you are sinful and must repent. Your prayer is invalid and must be repeated if you prayed Fajr with impurity intentionally, knowing of its presence. However, if you prayed with it forgetfully or out of ignorance, then your prayer is valid. Dry impurity does not transfer to dry places where you sat, and impurity does not transfer merely by doubt. The default state is purity, so beware of obsessive doubts.