I have a brother who married an illegal and has 2 kids with her o her home but ever since they got married she still goes and spends the weekends at her mom every weekend and some times weeks her mom picks he up and brings her around payda only and takes her back to her home now she is 31 yr old... and this has been 6yrs doing this.. never really stay home with my brotheer.. well my question is can she this be fraud marriage in her part and her mom? What can my brother do he is so sick with this and his inlaws and he wants his baby's please help any info asap thanks

Unless she is here illegally,then from what you have said she is just a user.
Sad to say there is no law against people doing that.
I would think twice about reporting her as an illegal as your brother could be implicated as well.
What about the children?
The legal person in the family needs to talk to the IS.

They've been married for 6 years, so she must be US citizen by now. This is family matter, and the one who should take action is your brother, NOT YOU. He should discuss his likes and dislikes with his wife and if he's not happy with the result, he should get a good attorney, file divorce, get child custody, etc.

Before thinking of reporting immigration fraud, consider the fact that if this is true, your brother could be charged for conspiracy and immigration fraud as well. The maximum penalty would be 5 years in federal prison plus a quarter million dollars fine.

6 years marriage, lives with him during the week, has 2 children with him. Sounds like a marriage problem, not immigration.

From immigration perspective, it is a real marriage. Your brother should have gotten her permanent residence and she should have filed for citizenship by now.