I'm not sure about the plural form of immovable (immovables). By the way, is "immovable" a word that English speakers use when referring to "real estates, properties etc."?
"Immovable" (short for "immovable property"), as a noun, is a civil law term used to speak of property that cannot be moved or carried away, such as real estate. Moveable property, on the other hand, can be moved freely (think of cars, computers, et cetera).
As an example of its plural form, "We prepared a list of all moveables in the sale agreement."
In the U.S., at least, the conventional term is "real property", as opposed to "personal property", which can be moved.