Is the ongoing relationship between the questioner and the girl unlawful after her parents and people have known for all these years that she is his wife? And is everything he has spent on her from his money considered unlawful for her? And is it permissible for him to continue with the marriage to her in court, yielding to her family's wish? And if he marries her and his family finds out what he has done and asks him to divorce her, should he abandon this marriage or marry her and divorce her without his family's knowledge?

What you have committed are major and most egregious sins. People's knowledge of this relationship does not validate it or make it permissible; rather, it is fornication (zina), for marriage is a contract with conditions and pillars. You both must sever this relationship immediately. If you wish to rectify it with a legitimate contract after repentance and ensuring no pregnancy (istibra'), there is no objection. What you spent on her, if it was a gift, is permissible. But if it was in exchange for sexual access, then it is the dowry of a harlot (mahr baghi) and forbidden. Marrying her is permissible under the conditions of a valid marriage. There is no sin upon you in marrying her with the intention of divorcing her later to cover her (reputation). The consent of your parents is not a condition for the validity of the marriage, and you are not obligated to divorce her if they request it without a legitimate Islamic reason.