Is it permissible to continue recitation and correct mistakes between two individuals who do not fully master the rules of Tajweed, or could that lead to sin instead of reward?

Great care must be taken in reciting the Qur’an, and adhering to all principles of Tajweed is obligatory. One who abandons it is sinful, for the Ummah is commanded to correct the pronunciation of the Qur’an’s words and to uphold its letters. Overt error (Lahn Jali) that alters the meaning is not permissible for recitation. If one is capable of learning, it is obligatory for them to refrain from reciting the Qur’an with error until they learn it. If they cannot find a teacher, they should utilize modern resources.