What is the ruling concerning my brother who suffered from psychological disorders that affected his worship and his dutifulness to my parents, and has now become regular in his prayers and acts of worship and has established an endowment for my parents?

The psychological distress of an individual does not remove their accountability for religious obligations unless they become irrational in their actions. In such a case, they are not held accountable, based on the hadith (definition): "The pen has been lifted from three: from the sleeper until he awakens, from the child until he grows up, and from the insane person until he regains his sanity." Neglecting prayer is a grave sin, and disobedience to parents is one of the major sins.