Answer
(Fatwa: 610/514/B=1433)
According to Islam it is not permissible for your brother to love a non-Muslim girl i.e. to develop friendship with any strange girl. Such love marriage does not last for long. However, if the girl accepts Islam believing it true religion and stands firm then her nikah if done on Islamic pattern with a Muslim boy shall be valid. Neither it is lawful for that girl to do nikah on non-Islamic pattern nor for you after she embraces Islam. After accepting Islam only Islamic system shall be acceptable.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband