A:
Cursing and insulting the parents is an act of undutifulness, which is one of the major sins. Allah (Exalted be He) says,
...say not to them a word of disrespect, nor shout at them but address them in terms of honour.
And lower unto them the wing of submission and humility through mercy, and say: "My Lord! Bestow on them Your Mercy as they did bring me up when I was young."
(Part No. 25; Page No. 240) Whoever curses and insults their parents should repent to Allah, treat them kindly, and ask for their forgiveness. However, their Salah is valid although they commit a major sin for cursing and insulting their parents. Moreover, such undutiful children have the right to inherit their parents because they are Muslims. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.