Is a marriage contract valid if the girl's guardian curses the religion, and is it permissible to congratulate the bride and groom without being certain that the father who curses the religion is indeed the guardian?

Cursing the religion of Islam is disbelief (kufr), and it is not permissible for a disbeliever to marry a Muslim woman. However, if the man repents from cursing the religion, then his guardianship (wilayah) becomes valid. And if he pronounces the two testimonies of faith (Shahadatayn) or prays, the default is that he is a Muslim, and his guardianship becomes valid. Therefore, there is no harm in congratulating the couple, and there is no need to verify the validity of the marriage contract. However, it is obligatory to advise the man, enjoin him to good, and forbid him from cursing the religion, which is one of the greatest abominations.