Not the daddy or is he ?

I have a friend who is with a girl that's "probably" his babymama. So they begin talking around August 2016 , she gave him an STD in September 2016 . Now she's 5 months pregnant , but the gag is she was sleeping around with people they both knew around that time the baby was conceived. I don't want to come off ass rude or something but what's the best way to tell my friend he needs to get a paternity test when this baby boy comes. Also, I find it so weird that she's having a baby when nothing but girls run in his family. It's only 2 little boys and the rest are girls. She don't even want to name the baby after him and won't give a reason why she don't.