Since your sister and brother had bitter experience in their marriage life, it doesn’t mean that you life will always be like that. If you are not confident and have fear in your subconscious mind then you will see only the negative things.
So just have a broad vision towards this world. Many couple are living happily and many couple are got married beyond their cast.
You first concentrate on your job. Don’t think unnecessarily. Don’t rely on online friends. Try in matrimonial websites. you will get very good partner who will accept your education and higher qualification and will take care of you very well in your religion itself.
All the best.