Is it permissible to use a hijab for protection from sorcery and harm, and is it considered a severance of kinship ties not to visit harmful relatives after they have been expelled?

Regarding the amulet (hirz): If it contains verses from the Holy Quran and supplications from the Prophet's Sunnah, scholars have differed on the permissibility of wearing it. A group of companions and their followers permitted it. This is the view of Imam Al-Qurtubi, Imam Al-Nawawi, Al-Hafiz Ibn Hajar Al-Asqalani, and Al-Allamah Al-Sindi. It is also adopted by the Hanafis, Malikis, Shafi'is, and one narration from Ahmad. They based their argument on the fact that the prohibition mentioned in the prophetic traditions does not include what contains the remembrance of Allah, but rather it is specific to polytheistic amulets.

Others, however, prohibited it. This is another narration from Ahmad. They based their argument on the generality of the prohibition against amulets, blocking the means [to evil], and what might result from wearing them, such as the desecration of the Quran. Al-Qadi from the Hanbalis held the view that it is permissible if one believes that benefit and harm come only from Allah.

As for your second question: If your uncles are as you described in terms of causing harm, then there is no sin upon you in cutting ties with them and keeping away from them.