Should CPS become involved?

We have a family friend (late 20’s) with 3 children ranging from newborn-5yrs old. My mom has taken her into her home off and on for the last few years. See, her husband is a drug addict and sex addict and is constantly cheating on her and paying girls for sex. Even on family vacations. I have no proof but we believe he may also be physically abusing her. She is a victim of abuse and it hurts me to watch her go back to him, then back to my mom for sanctuary away from him. She also is very religious and does not believe in divorce. Unfortunately when she does go back to him she leaves the 2 older kids with my mom to care for most of the time. The kids have a lot of behavioral issues due to not being shown love by both parents. They look at my mom as their mom at this point and cry for her rather then for real mother. They are thriving in my moms care. When their mom is around, they break down and the behavioral issues come back. I don’t live with my mom but my younger sisters tell me how she spanks them for no reason, only because she herself is overwhelmed trying to “save” her marriage. At this point I feel as thought she cares more for her husband then her own children.

My mom is exhausted. She’s been helping her for years, with money, a place to live, free child care. She is so tired of her always going back to her dead beat husband, especially with him not trying to change at all. So she’s helped her apply for a woman’s shelter and now she’s on a wait list.

At what point should CPS get involved? The kids are currently safe, fed, and clothed thanks to my mother. They won’t be in danger as long as they have her, but at what point does this turn from domestic violence to child neglect? Without my mom they would be homeless, seeing as her husband has lost the apartment due to not paying rent and the mom doesn’t have a job.

She was a dear friend of mine when we were both teenagers and I see what is happening and I’m start to become concerned for her children’s safety. Yes she’s is being abused and I’d hate to see her kids taken away. But this can’t keep going on like this… my mom can’t be here forever to take care of them and the friend is not doing anything to make life better for herself and the children.

Update: my mom said it’s to much for her to continue housing them/feeding them/financially supporting them if she just keeps going back to him and doesn’t want help. My mom has found her resources and helped place her on the wait list for a woman’s shelter. The mother of the children will not go to therapy, and has been told that she can get a divorce by a pastor yet she loves him to much to leave which is also why she keeps playing the religion card. She refuses to get a job even thought my mom said she could baby sit if she got one. During her pregnancy with one of the children her husband drugged her to try to get her addicted but she never reported. One thing I completely forgot was when she was living with him and the kids joined her, when her son came to visit my mom he arrived with severe bleeding diaper rash and she wasn’t cleaning his penis so he would get what my mom says was infections/puss coming from his penis. She also does not change his diapers as often as she should so unless my mom is there to change him, he just hangs out in his own poop filled diaper all day. My sisters claim that the spanking has gotten out of control as well and that she will hit him over little things.