Step father cheating on my mom

Just a quick summary my step dad move into my mom apartment some years ago, he quickly married my mom so he can get his green card after that was processed he quickly filed to bring his kids into the country my mom help him with all of this including the expenses. His 3 kids came to live with us and currently my step dad is in a lot of debt for a bunch of reasons. One of the biggest debt he’s in was him buying a car behind my mom back and not speaking to her first before going about it. So now him and his kids all live with us in my mom place this man doesn’t pay rent because he claim he’s in a lot of debt and don’t have money. So my mom is left to pay every single bills in the house herself even while taking care of his kids because majority of the time he don’t make sure there’s food in the house for them, clothes and other necessities they need. Some months ago my mom found a bank statement in there joint account of him going to a motel close to his job. He denied everything and the charges wasn’t one time it was multiple times in different months. He lied and said he paid for a motel for his friend when his friend works and have a whole wife. Then yesterday my mom got home from work at 1 AM. She came home to see the husband sleeping but he fell asleep while his phone was unlocked. When my mom looked through it he was messaging a girl name Mecca, saying babe I miss you and when my mom confront him about it at first he said he doesn’t know what she’s talking about, then he tried to gaslight her, then he said that’s how they talk in Nigeria. He lie so much. Every time he get paid he take all the money out of his account and it seem he put it in a different account that my mom isn’t aware of. This guy is using my mom, cheating on her while she pay the bills alone and get no help from him and have to also help take care of his kids. Now today my mom is telling me they talked about it and when I asked her what he said about the Mecca situation he said it was all a misunderstanding that, that’s how they call each other in their country and my mom basically settled for it. This man also doesn’t care about me and my sister only about his kids. Then my mom got this tight bond with his kids while he don’t even care about hers. This whole experience has been very draining on me I’m just really trying to finish up school so I can get a career for myself and leave this place.