Your text is correct. Both "in the same school" and "at the same school" are correct and natural. "Her brother and she" is plural, so "[they] are" is correct. "Her brother and she" is less common than "she and her brother." "She" is the word with more emphasis. Here is a Google N-gram that shows "She and her husband" is about ten times more common in fiction (descriptive prose) than "Her husband and she." https://books.google.com/ngrams/graph?content=she+and+her+husband%2Cher+husband+and+she&year_start=1800&year_end=2000&corpus=16&smoothing=3&share=&direct_url=t1%3B%2Cshe%20and%20her%20husband%3B%2Cc0%3B.t1%3B%2Cher%20husband%20and%20she%3B%2Cc0

In America, we have a trick where if you remove “her brother and” from the sentence, or ‘the other person’ which leaves you with ‘she are in or she are at the same school which is grammatically wrong, which you would say “She and her brother go to the same school” which is the most grammatically correct.