I don't think husbands son is his.

Hi! I am actually writing this for my BFF bc she is totally confused. She has been married for almost 4 years (dated 2) to a man who has 2 kids from 2 different women. The problem is his son (2nd ex wife). This ex wife is crazy- constantly playing mind games, bashing them both to son, and threatening court, etc (he pays child support- she wants more). The thing is he has caught ex cheating before and wasn't even sure baby was his until he saw him at birth and everyone said the baby looked just like his father. Personally, I think that's crazy because too many babies look alike at birth. Anyway, the son looks NOTHING like dad now (looks like moms first son and a little like mom). Neither one of us believe blood is thicker than water and both know you can love a child like your own who isn't. The problem is she is COMSTANTLY threatening him and has made the son a manipulative little tied (if dad doesn't do what he wants then he won't go over. He's 14- too old for that crap). I think she should do a secret DNA test and see -if it's not his she can tell wife the game is up- that for sons sake it doesn't have to come out but to stop the threats and manipulating. She's worried husband will get mad but same time aggravated that he won't grow some balls with both of them.
Before you start- yes, we both know he has raised him and he will always be "dad" to him so please don't start bashing me with that crap. The point is this man has gone above and beyond for this child and they both still threaten or manipulate him. It affects everyone else in the family and enough is enough. She has talked to him about seoerating because she's tired of the drama but he begs her not to. She loves him but is tired of dealing with the drama and manipulation the constantly dole out.
What do you think? Anyone have any solid advice to help her without bashing her/ me? I'm asking for advice for her- not bashing liberalist.