The first sentence is correct, “in the room” modifies the noun/object “book”. The second sentence is also correct “on the campus” modifies “father”. The third is also correct the preposition “in” does modify “the class” since the class can be in April. Example: I have an exam in December.
The third sentence is not correct, the first simply indicates where they will meet, the second indicates the father’s location while the fourth shows that they are confident and sure of the location of the father. Example: we were to met at the train station, however he was not on the train when I got there.
The sentences are correct, but one can do away with the article “the” to have “on campus” “on the campus” modifies “see him” since “seeing him[who] on the campus. In the second “on the campus” modifies “the guy”. Yes one can have two prepositions and interchange them to have the same meaning. “On the desk” modifies “a book”. Example; last night we saw him on campus
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