Stepson's friend continuously says racist remarks at my house. Should I keep my mouth shut?

My husband (white) and I (black) share custody of his two teenage kids with his ex-wife (white). My husband and I only live a five minute bike ride away from his ex and the kids split time between each house. My husband and I also have a toddler son together.My stepson, who I will refer to as Nick, has a couple of friends that he often brings over after school. Nick is 14 and is a pretty good kid, but he is a little social awkward, as are his friends. We don't allow the kids to have televisions in their bedrooms, so the boys will normally hang out in the living room to play video games. I recently overheard one of Nick's friends (Jake) say that they need to "find all the (n-words) and kill them." I was shocked, but didn't say anything at first. It got worse and I told Jake that we don't use that language in our house. He apologized and didn't use it again.Jake came over yesterday and used the n-word again. I explained that we don't use that word and he told me that his mom said he could. I told him that I can't control what words he uses outside of my house, but we don't allow that kind of language in our house. He threw a little fit and said that he won't use it anymore and I left them alone. Nick later told me that Jake continued to use the word and that it made him uncomfortable.I'm just not sure what to do. My husband and his ex say to let it go. I am considering calling his mom, but that seems weird to do at this age. It's just not a word I want to be used in my home, especially with a toddler in the house, and I feel like that should be respected. Am I wrong here? via /r/Parenting http://ift.tt/2ftKmxz