Everyone is looking at us.
In the above sentence, "to look" is the verb, "everyone" the subject. Is "us" a direct object or indirect object?
How do you find the DO and IO?
Us is here the object of the preposition at, not a direct or indirect object.
The way to tell apart direct and indirect objects is quite simple: a direct object has the verb performed directly upon it, and can be the subject of a subject-verb passive sentence (I saw the man becomes The man was seen), while an indirect object is generally something that receives the DO.
Example: I gave the man a cake. In this sentence, it would make sense to say "A cake was given," but not "The man was given." Therefore, the DO is the man and the IO is a cake.
In your sentence, it would not make sense to passivize it as "We are looked", so the word in question is no DO. Without a DO, an active clause cannot have an IO; therefore, us is neither, instead the object of a preposition.