Is it permissible to remove the niqab to please parents and suitors, or is it obligatory to refuse that to please Allah?

If removing the niqab is for a sharia-compliant viewing (for marriage proposal), then it is permissible, and you must respond to your father's request. However, if the removal is permanent, do not comply, because the niqab is obligatory according to the most preponderant scholarly opinions, especially in these times when immoral people have become numerous. There is no obedience to a creature in disobedience to the Creator. You must be patient with Allah's command and treat your father kindly with good words.