thank you for sharing your question with the Wefugees Community!
I am not an expert on this field but maybe I can help you with some general information:
In general, family reunion is only an option with your closest family members like parents, underage children or your spouse. For family members like - in your case - siblings the chances are not really good. It´s only possible unter the prerequisite that you would face an extreme hardship if the reunification did not take place. As you can imagine, it is not easy to prove this - it applies mostly when the family member is very sick and needs special care. I don´t know much about your case but from the little information you gave me, I am not sure that this is an easy way for you to stay in Germany.
But besides from family reunion you can f. e. try to get a residence permit through work after your studies. Or if you decide not to finish university, maybe you want to do a vocational training instead ("Ausbildung"). Or maybe you even qualify for a EU-Bluecard (since you have a bachelor degree)?...Maybe these are options for you? Via this page you can take a closer look at these options. It also provides additional informations about getting a residence permit in Germany:
I hope this information was helpful for you. Please don´t hesitate getting back to the Wefugees Community if you have more questions!
All the best
Note: Please keep in mind that we can´t provide qualified legal advice via the internet and that any information given can´t replace such legal advice.