What is the reward for continuously caring for mentally ill siblings in all aspects of their lives, and does reciting some adhkar and supplications, which are said to grant entry to Paradise, compensate for shortcomings in performing obligatory duties and acts of worship?

Caring for mentally ill siblings is a form of beneficence through which one attains Allah's love. It is one of the greatest forms of beneficence commanded by Islamic law, second only to beneficence towards parents, especially if they are orphans. The invocations for which Allah has promised paradise to their reciter do not substitute the performance of obligatory duties.