What is the supplication to be said to stop the evil of aggressive paternal uncles and their children, and is it obligatory to maintain ties with them despite their actions?

If your relatives wrong you, warn them of the consequences of injustice and seek help from those who can influence them. If that doesn't work, then refer your case to the authorities. It is permissible to supplicate against the oppressor to the extent of their transgression, without exceeding it, but it is better to refrain from doing so. Maintain your morning and evening remembrances, and we recommend "Fortress of the Muslim" (Hisn al-Muslim). Maintaining kinship ties is obligatory as long as it does not result in harm, even with those who sever them, for the one who maintains ties is not the one who reciprocates, but rather the one who maintains ties when his kinship is severed. Responding to evil with good brings affection and protects against the evil of Satan.