“que < A >” and “que < B >” are components (propositions subordonnées) of the sentence that replace a noun used as direct object of the verb “croire”.

In other words, the logic behind such construction is:

<sentence> = <subject> <verb> <direct_object1> and <direct_object2>. 

where:

 <direct_object1> = que <A>
 <direct_object2> = que <B>

Two “que” are necessary when the verbs are different:

Je crois que Jean est gentil et que Marie aime danser.

If it is the same verb, you can put one (don’t repeat the verb) or two “que”:

Je crois que Jean est gentil et Marie drôle.
Je crois que Jean est gentil et que Marie est drôle.