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 is His Slave and Messenger.
It is a grave danger to deny these matters as the evidence for them has been confirmed in the Quran and the Sunnah. Imaam Ash-Shawkaani has written an essay called At-Tawdheeh fi Tawaatur ma Jaa’a fi Al-Ahaadeeth fi Al-Mahdi, wad-Dajjaal wal-Maseeh. So, it is an obligation to believe in the descent of 'Eesa (Jesus) and the emergence of the Mahdi and the Dajjaal so as to believe in what Allaah and His Messenger have said, and it is not permissible to deny any of that.
However, not everyone who rejects it is ruled a disbeliever, as some may have a misconception or misinterpret the texts. A Fatwa from the Permanent Committee about ‘Eesa reads: “It is proven with evidence from the Quran and the Sunnah that 'Eesa was not killed and he did not die - rather, Allaah took him up to Him alive - and that he will descend at the end of time as a just ruler in this (Muslim) nation, so whoever says that 'Eesa died and that he will not descend at the end of time, he has indeed contradicted the Book of Allaah and the Sunnah of His Prophet and he is absolutely wrong and he is ruled a disbeliever, after the truth is conveyed to him and after the evidence is established against him, as he is denying what Allaah and His Messenger stated.” For more benefit, please refer to Fatwa 8106.
However, one of the greatest forms of kindness and dutifulness of children to their parents is to teach them the truth in order to bring them back to the straight path. You should know that children are obliged to be dutiful to their parents even if the latter are disobedient Muslims or disbelievers as we have already clarified in Fatwa 85180.
For more benefit, please refer to Fatwa 90497.
Allaah Knows best.