All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If your mother is as you have mentioned, then she is incurring grave evils on herself especially with regards to forsaking the prayer. Neglecting the obligatory prayers is indeed a grave sin. Some scholars even held that abandoning the prayer is an act of disbelief that takes the doer out of the realm of Islam even if it is done out of neglect.
It is odd that your mother continues to commit such sins even after performing Hajj. Indeed, the ultimate objective of the acts of worship is the purification of the soul and refinement of conduct. The fruit of performing acts of worship is attaining Taqwa (piety and righteousness). Allaah, The Exalted, says (what means): {O mankind, worship your Lord, who created you and those before you, that you may become righteous.}[Quran 2:21]
The sign of acceptance of one’s good deeds is that he is guided to do more good deeds. Allaah, The Exalted, says (what means): {And those who are guided - He increases them in guidance and gives them their righteousness.}[Quran 47:17] This is why scholars held that doing more good is a sign of acceptance of one’s good deeds.
It is also strange that your mother is so harsh towards her children. A mother is commonly passionate, loving, and keen on the safety and interest of her children; a mother would not curse her own children or wish that they were dead.
In any case, our first advice to you is to constantly be patient. Patience is the optimal source of comfort when affliction befalls. It is a great means to draw closer to The Lord of the earth and heavens, and its consequences in this worldly life and the Hereafter bring contentment. Therefore, you should to be patient and enduring. Please refer to Fatwa 83577 for some religious texts on the merits of patience.
Moreover, you should supplicate Allaah to set your mother right, guide her to sound judgment, and shield her against the evils of herself and evil deeds. Certainly, supplication is the best means for accomplishing one’s objective. Our Lord, The Most Generous, commanded us to appeal to Him and promised to answer our supplications. In fact, Allaah, The Exalted, likes His slaves to supplicate Him and dislikes it when they dispense with turning to Him in supplication; He says (what means): {And your Lord says, "Call upon Me; I will respond to you." Indeed, those who disdain My worship will enter Hell [rendered] contemptible.}[Quran 40:60] Abu Hurayrah reported that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Verily, he who fails to supplicate Allaah incurs His wrath.” [At-Tirmithi]
You should know that you are obliged to be dutiful towards your mother regardless of her abuse and harshness as we explained in Fataawa 85542 and 92315; it is important that you refer to them. Be careful of harming or wronging her in the slightest manner for this is considered undutifulness. Please refer to Fatwa 87856.
We deem you far above refusing to forgive and pardon your mother abuse and maltreatment. Indeed, pardon and forgiveness are required in one’s relationships with all people and are more emphasized, and more rewardable, when it comes to the mother. For more benefit, please refer to Fatwa 84351 about the merits of pardon.
On the other hand, your mother has no right to object to you marrying a girl from your father’s family as long as the girl is righteous and well-mannered. In that case, you are not obliged to obey her and abstain from marrying that girl if your mother’s objection is merely based on her personal preference and wish, or out of foolishness. Please refer to Fatwa 131695 about the limits of children's obedience to parents.
However, if you chose to give up marrying that girl so as to avoid your mother’s anger and harm, you can do so. You can also opt for that choice if you realized that it is to your best interest.
Note that engagement is revocable; either of the two parties may revoke it as underlined in Fatwa 82215.
We ask Allaah to bless your mother with guidance, reason and discretion, to soften her heart, bless her with noble manners, and bless you with her good company for long years. Verily, Allaah is the All-Hearing and answers prayers.
Allaah Knows best.