What to do about niki and leah?

ok so me and my boyfriend have been together for 9 months now but we have a problem. His ex girlfriend is telling him that her 11 month old daughter is his just now. he didnt even know she was pregnant or that leah was born. his ex girlfriend niki really likes him and wants him back and recently her and her boyfriend (who is supposedly the babies father) broke up and she doesnt have a job. it seems like she wants to make every excuse not to take a DNA test. She is known to cheat and lie and hide things. So what do you think?