18 year old disrespectful

My sister is 18 and has 2 under 2! She lives with my mom and is beyond disrespectful and a disgusting pig! Today I went over for only 20 minutes before I decided it was time to leave because that’s literally how quickly shit hit the fan!

My sisters two kids were up so my mom asked if my daughter and I wanted to come hangout for a bit - I said yes, because we hardly go over there for these exact reasons! So my mom asked my sister if they could come out of the dark ass room they sleep in to play mind you it was 9:30 am - they had full diapers & one of them was pooped! They were hungry and ready to get up - so my mom asked if she could take them out and get ready for the day. My sister disrespectfully said NO and to close her door, my mom then responded can she at least turn on the tv for them - my sister then disrespectfully replied NO.

So my daughter and I were in the living room flabbergasted with my still screaming nieces who obviously wanted out - so my mom gave in and opened the door for them - changed them and put food on - my sister came out of her room and took them back in her room, where they are probably still there screaming because I told my mom I would like to leave because this is too much stress for me I’m almost 5 weeks & my daughter doesn’t like this because my husband and I do NOT ever act like this at home.

I had a physical altercation with her in January because she punched my mom in the face & we are sisters, sometimes they fight - I don’t think a fight should ever be because you own sibling punched you mom though - we got over it but she is getting absolutely disgusting and beyond manageable. My mom is devastated at how she turned out & wants to throw her out but afraid for the kids. My mom can NOT take them it’s out of the question because she is sick with juvenile diabetes, fibromyalgia, has club feet, the list goes on - last may I went to the ER with her and they said if she doesn’t start taking care of herself and her sugar she is going to die.

My sister hasn’t graduated high school, doesn’t have a job because no one wants to baby sit because her kids can be a bit hard ( because of their surroundings, their tantrums are out of control ) I love my nieces but I’m not in a place to take them either - my sister threatens her kids with adoption and tells them fu* them and that she hates them when they don’t stop crying!

I’m scared she will hurt them - cps gets involved and always dismisses the cases! What can we do, my mom doesn’t want to kick her out because she’s frightened for the children & I understand. But my sister leaves huge disgusting messes of food and dishes all over the house including cereal bowls with half eaten cereal on the tub ledge and ONLY feeds her kids snacks!

What can we do for this girl? Running out of options, she needs serious help. I’m wanting to help from a distance I can’t do anything physically.