it must always be clear what or who the pronoun is referring to. It doesn't matter where the pronoun or the noun is referring in the sentence (the pronoun does not necessarily modifies the closest noun)
Tom and Jim went to the club after he took a shower
Who took a shower? Since you have two nouns, it's impossible to know which one.
If, in the other hand, you have a plural noun and a singular noun and you use a singular pronoun to refer back to the singular noun, your sentence will be correct, since it is clear who are you talking about.
In the first example you provided, the sentence has 2 plural nouns (rhinos and tourists), therefore, you can't use a plural pronoun, because it will not be clear who are you talking about, regardless if it's obvious or not (not even a 6th grader will think that tourists have horns).
In the second example, majority and power stations are plural, thus, you can't use they (again, it doesn't matter if power stations think or not).
Also note that pronouns that refer back to a a possessive noun are incorrect. Consider:
John's mom wants him to clean his room.
Him is incorrect because there is no reference for John, only for John's mom.
Hope this makes sense.
I would think you would benefit from reading MGMAT's SC
guide. Good luck!