Problems with my children's stepmom?

My exhusband has custody of our three kids 16,13 and 11. My oldest son has reported problems for quite awhile now, he says she hates him goes out of her way to make his life a living hell cussing wanting him to hit her so she can call the cops on him wrote on his wall in big letters what a ahole he is he trys to stay out of her way but she goes looking for him. My 13 year old sticks up for her and blames everything on his older brother but then he tells me a couple days ago that his stepmom told him that she doesn't want any of them the only reason they are in her life is because of their dad. My youngest son trys so hard to please her but she freaks out saying that they all will be homeless dad and sons because she is the one that makes the money. I don't want to overreact but when I talk to my exhusband all he says is that my oldest son is full of it and blames everything on him. The kids are great when they are here all summer every weekend spring break no signs of terrible teens.