He married a second wife and they became Muslim – what should he do with his first wife?

Question I would appreciate if you can give an immediate answer to this question which has been bothering my new brother who just professes his faith in Islam. A man has had a relationship with a woman bearing 2 children during their marriage relationship way back on their own country. In the course of time, the man got a job in Saudi Arabia for contractual basis, leaving his wife and children behind. At the time the man was working in Saudi Arabia, he met a woman and had a relationship with her which bores them 1 child. A civil marriage ceremony was consumated without the knowledge of the first wife which he leave in his own country. Now, the couple who both works in Saudi Arabia recently embraced Islam. Since both are new in the religion, fearing they might commit sins/wrongs which is against the teaching of Islam, could you please give us your advise on the following: 1. what is the Islamic ruling about the relationship mentioned? 2. what is the man...