Is it permissible to sabotage the marriages of one's female cousins, after the grandmother and aunts worked to separate her sons and drive away suitors from her daughters?

The matter of marriage is in the hand of the father. If he is absent, then the paternal grandfather, then the full brother or paternal half-brother, then the nephew, then the paternal uncle. As for what the grandmother and maternal aunt do in deterring suitors, this is forbidden and not permissible, because it is corruption, and Allah does not love the corrupters. It is not permissible to counter this evil by corrupting the marriages of those who have married. Rather, evil should be repelled with good, for Allah Almighty says: "Repel [evil] with that which is better." And it is mentioned in the Hadith: "None of you believes until he loves for his brother what he loves for himself."