What is the ruling on supplicating against brothers or sisters who are sinful, undutiful to their parents, and excessive in sins? Is this considered undutifulness?

Supplicating against people who commit sins is a matter of scholarly disagreement. The preponderant opinion is that it is impermissible to supplicate against a specific Muslim who has fallen into sin, unless he is an oppressor or causes harm, in which case it is permissible to supplicate against him to the extent of his injustice. However, refraining from such supplication is better, and it is preferable to supplicate for his guidance. If the one supplicated against is a relative, the matter is even more reprehensible, because supplicating against him is considered a severance of kinship ties, which is a forbidden sin.