Should I not believe my brother's claims about our mother's mistreatment of him, despite my prior knowledge of our mother's behaviors and my past experiences with her, which confirm the likelihood of his claims being true?

Abusing a mother does not justify abandoning her or nullify the duty to honor her. The matter can be verified by asking the mother and reminding her that the money spent by the father should be given to the poor son among them to the extent of his needs. If the father is unable and the mother is wealthy, she is obligated to spend on her poor son. Some scholars have permitted having ill thoughts about those whose actions are丑恶. Among them are those who consider the forbidden type of suspicion to be that which is spoken, not that which occurs in the heart. Therefore, there is no sin if its truthfulness occurs in the heart.