Pjiang老師,請幫助我的朋友

He is working in USA with Green Card. His 12-year-old daughter came here with him recently. He has divorced long time ago in China. He is planning to apply for visiting visa for his parents or his ex-wife. Maybe he will re-marry to his ex-wife.

Questions are, who will have higher chance to get the visiting visa, his parents or his ex-wife? His daughter invites her mother(my friend's ex-wife),better than he, right? How to prepare the document for visa applying?

Thanks a lot.