Manipulating ex girlfriend

So my husband has a ex girlfriend and they have a daughter(who is 6) that the mother is maninpulating she into saying her 2 teen brothers that are only my husbads kids that they are abusing her(smacking, pushing, grabbing...ect) now she has been show up to our house with bruses and when asked she blames it on the boys doing that to her. Let me mind you we just got done with court on april 5th and we got more time(she was not happy about that)

We are truly scared that something is going to happen whether it is her getting takin away or the boys going to jail over it. They boys love their sister and she is the only sister They are gentle with her they know she's a girl and only 6.

She has tried pulling this before. And has convinced her that she saw her older brother jacking off. And the 6 year old said the words jacking off. They're never in a room alone or even alone for that matter.

We just want our happy family. I have a baby on the way. I looking for work. We just fought to see her more. We just want to have our little happy family in this house.

What can or should we do