Are you religiously sinful for sheltering your sister and her children and assisting her with divorce proceedings from her oppressive husband whom you failed to reform?

Resorting to divorcing a woman from her oppressive husband is the last resort. Before that, an attempt should be made to reform him by advising him and clarifying the religious ruling to him. If that does not work, his case should be brought before influential people from his relatives to bring him back to his senses. Otherwise, his case should be referred to the Sharia courts to examine the matter and decide on reconciliation.