Is the employee obligated to continue educating his colleagues despite their negligence, or would ceasing to educate be considered a breach of promise or arrogance?

Fulfilling a promise is recommended. Since you attempted to fulfill your promise to your colleagues by teaching them what would benefit them, and they did not respond, there is no blame upon you for stopping due to the lack of benefit, even though patience in teaching them would be better. These brothers must learn what qualifies them for their work if they are not proficient in it; otherwise, their earnings would be unlawful.