Am I sinful for severing ties of kinship with irreligious family members who harm me in my religion and my marital life, especially since my presence with them compels me to listen to what displeases Allah, even reaching the point of insulting the Divine Self, the religion, and the Companions?

Cursing the Lord and religion is a major act of disbelief (kufr akbar). You must call your family to abandon this disbelief and return to Islam. You are obligated to be dutiful to your mother and treat her kindly, even if she calls you to shirk (definition) (associating partners with Allah), but you are not required to live with them in a dwelling where sins are committed. Do not be discouraged by your family’s attempts to dissuade you because of your adherence to the Shari'ah. Obedience to parents is obligatory in what is good, not in disobedience. You must treat your family kindly, advise them, and pray for their guidance.