___ not allowed to visit the patient in ICU.

The correct answer is "their." In this context, "their" is used as a possessive pronoun, indicating ownership or association with the individuals who are not allowed to visit the patient. The sentence implies that a specific group of people (the individuals in question) has a connection to the patient in the ICU, thus necessitating the use of a possessive form.

The other words do not fit into this context. "The'ir" is not a standard English word and doesn't exist in this form. "There" refers to a location or place, making it unsuitable as it does not indicate possession. "They're" is a contraction for "they are," which also doesn't convey the possessive sense required in this sentence. By using "their," the sentence correctly communicates that it is those people's right or ability to visit that is being restricted.