1. In case your mother have acquired the property out of her earning, she can transfer to anyone be it a man of straw.
2. If your mother have acquired the property which your father have acquired out of his earning by way of gift, she is again entitled to do whatever she likes.
3. But if your mother have acquired the your ancestral property, you can claim your rights. Moreover if your mother have acquired the property willed by your deceased father, you can challenge the will.
4. Definitely you can sue a mental harassment on your brothers and mother.
Before processing anything please consider for the searching reports of the property from the registrar's office.