Does the deceased suffer from his mother's curses and anger towards him after his death, and does her anger prevent him from entering Paradise?

If your father was upright and well-praised by people after his death, this is an indication of his good خاتمة (final outcome), as evidenced by the hadith (definition): "You are Allah's witnesses on earth." Imam An-Nawawi also stated that people's praise of the deceased is an indication that he is among the people of Paradise. As for what your grandmother says, it does not affect your father. It is advised to disregard it and focus on what benefits him, such as supplication (dua) and charity (sadaqah (definition)).