Honestly, whether she knows it or not, I would call and make a call to the SPCA at the same time about those animals. The living conditions sounds like the kids could get REALLY sick, a home like that isn't suitable for those animals let alone those poor kids. She's being a lazy parent and not looking after the well-being of them.
It's all about the safety of the kids, and if they haven't been really sick yet because of those living conditions, they're lucky. Get help for those kids please, if she's not willing to take care of them, someone has to speak up for them.
Find a local professional that deals with hoarding and contact them. Get information and set up an appointment. Sit down with your sister and give her the brochures - tell her that you will care for the kids while she's there, and how concerned you are for her.
Tell her that if she doesn't get help, you have no choice but to call authorities, as it's THAT bad. If you feel it would work, call in more members of your family and have an 'intervention' of sorts where you all stress how truly important this is, and how you want her to get help, and how you will all support her while she gets it. The fact that she hides it means she KNOWS she has a problem.
It sounds like she is hoarding animals and garbage - not just being messy. Hoarding is a mental condition that she needs to address - before it gets even worse and her kids ARE taken away. She is likely fearful of this anyways (which is why she doesn't let people in) - and stress the fact that it's just a matter of time before SOMEONE notices.
It's a danger to their health, and if there is ever a fire, a danger to getting them out alive. She needs HELP. Give her a timeline and offer to help (again) and INSIST she get treatment or you WILL call authorities, purely because you love those kids and they need help too - before they think it's normal.
Book the appointment FOR her and MAKE her go - and if she refuses, then as much as it sucks, you gotta do what is best for the kids. Perhaps you can ask CPS about YOU taking custody of the kids, or someone else within your family - so they're not put in a strangers home. All the best to you - hoarding is a tough thing to deal with, as the hoarding itself is just a symptom of deeper issues.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.