Is it permissible for a father – who curses Allah and dislikes the sheikhs – to pay Zakat al-Fitr on behalf of his children?

If your father repented of blaspheming Allah and started praying, then he is a Muslim, and Zakat al-Fitr is obligatory for him, for himself and for those whose maintenance is his responsibility. However, if he persists in blasphemy, does not repent, and does not pray, then he is an apostate.

Scholars have differed on the obligation of Zakat al-Fitr upon a disbeliever for his children or those whose maintenance is his responsibility. The preponderant opinion is that it is not obligatory for him. However, in the case of an apostate, there is a narration stating that it is obligatory for him.

Based on this, if your father, while being a disbeliever, paid Zakat al-Fitr on your behalf, it is valid for you.