Is it permissible to accept a suitor for my sister, even though he sometimes misses Fajr prayer and needs to review the Qur’an?

The Islamic Sharia (definition) encourages choosing a spouse who possesses faith and good character. Faith is the basis for fulfilling rights, and good character is the basis for harmonious companionship. If the young man is a memorizer of the Qur'an and has good character, and his sleeping through the Fajr prayer is not due to negligence, then this does not indicate a flaw in his religiosity. This is based on the Prophet's (peace be upon him) saying: "There is no negligence in sleep. Rather, negligence is on him who does not pray a prayer until the time for the next prayer comes."

However, if his sleeping is due to negligence and causes him to miss the prayer's time, then it is not permissible to marry your sister to him unless he repents. But if what is meant is that he misses the congregational prayer while still performing the prayer within its prescribed time, then there is no harm in marrying him, while encouraging him to perform it in congregation.