Worried for my nieces' safety. Step-sister is a severe alcoholic, and a 5-year-old is left taking care of the toddler. Is it time for CPS?

I’m coming to you all today for some urgent advice on a family situation that has reached a breaking point.

Yesterday, my mom received a FaceTime call from my step-sister’s 5-year-old daughter. When my mom answered, the 5-year-old was naked (said she’d just used the bathroom) and her 2-year-old sister was crying in the background. The 5-year-old told my mom that she was having to take care of her little sister until "Daddy came back inside from mowing." She then explicitly said that "Mommy drank a lot of mommy juice that makes Daddy mad when she does that," and that Mommy "messes up a lot" and gets mad easily when she drinks, so she has to take care of her sister.

My step-sister has a long, documented history of severe alcoholism. In the past, my step-dad had to pull strings to keep her out of jail, and she was forced to have an ignition interlock (breathalyzer) installed in her car (long since removed). I thought she was getting better because the drunk phone calls to us had slowed down, but it’s clear she is just hiding it or drinking while parenting.

We have been family for about 25 years, so this isn't a new dynamic. We have watched this cycle play out for decades, and because of that long history, everyone in the family is walking on eggshells. We’ve tried addressing this before over the years, but it always backfires:

• Last time we expressed concern, she cut us off for a while.
• A few years ago, a cousin wrote her a letter trying to talk to her; she ignored him and threw the letter away unread.
• My mom and aunt looked into doing an intervention, but a treatment center director actually talked them out of it, saying it would just cause her to put up walls and that she won’t get help until she wants it.

Right now, my mom wants to write her another letter, but because of our 25-year history, my step-sister knows exactly how to use leverage. I know she will just use the kids as a weapon and cut my mom off from seeing them completely. The codependency and enabling in our family run incredibly deep. I also feel like her husband is completely enabling this and failing to keep those little girls safe if he’s outside mowing while she is completely incapacitated inside with them.

I am sick of this, and I am terrified for these kids. I feel like if I do nothing, I’m going to end up attending a funeral for one of these girls. Because I don't personally spend a lot of time with them, she can't really punish me by restricting access. I feel like I'm the only one in the family who is in a position to take extreme action without fearing her backlash or worrying about her weaponizing the kids against me. An outside force feels like the only thing left that might actually break this cycle.

I’m seriously considering calling CPS because I don't know what else to do to guarantee their safety. I’ve also thought about inviting her to lunch to confront her directly, but history shows she will just deny it, lash out, and put her guard up.

I have an appointment to discuss this with my therapist this Friday, but in the meantime, I need outside perspectives from people who have been through this.

• Is a CPS report the right move here, or will it make things worse for the kids?
• If I do call, how anonymous is it really, and what should I expect?
• Are there any other courses of action I’m missing?

Thank you in advance for any advice.