Are my niece and nephew being abused

Hello I'm not sure where to ask this question so I'll just ask here. My niece and nephew are in the ages of 13 to 15. They're good lovable kids. They always have been. There's so much to say it's almost overwhelming. My sister is in her late 30s. She's a very narcissistic person. She got money from her divorce through various things involving my ex brother inlaw. She was in the 100ks at that point. She ended up buying a car. Her kids are now living in a small apartment always asking mom why did you not buy a house and bought a car. Her car was about 45k. House down-payment would've been 65k to 120k. Instead she spend 75% of that money on house decor, shopping and the car. Now she's left with quarter of the money. She works earns about 3000 per month. She gets chold supports and alimonly. often times buys things for my niece thinking she could buy her way through without communicating with them. I picked up my niece yesterday because she was emotional the day prior. My nephew ended up sneaking out and my sister got a call at 9 am from the mother of his gf she sounded very upset. They had intercourse which really upset everyone. He was banned from seeing this girl and she changed schools immediately. However my nephew promised my niece he would not do such a thing ever. They're kids I guess they talked about it. But my sister decides to tell my niece and she immediately breaks down. She texts me and says is this true. I couldnt lie to her. Her mother kept refering to it when she was just mad at him for it. Also my niece may have overheard them talking. But still the fact that she wanted to tell my niece about this really bothered me so i confronted her she said oh well its because i wanted her to know. Thats such a personal things regadless and also its not your job to tell a child. My niece calls me and we talked she cried very hard and said my dad left me and did the same, my mom keeps looking for men and leaving me, my brother did this and lied. She's a very emotional, emphatic kid. I'll go into detail a bit her father he's a nice man and all to her but it'd very hard for her to trust him again right now. She stated she will always love him and always want him in her life. Same for her mother. My sister finds these men on tinder. She doesn't bring them around the kids but sometimes she talks to her very loud friends and gets super loud and unfortunately the kids can hear her talking and then they confront her cuz they're concerned. Then says yea so what. She also tells the kids she had sex and she has a bf idk why. Also this isn't the only guy she's slept with and told about.  Oh yea forgot to mention she also says things like I hope you guys die, I hate you guys, and I wish you were never born. This hurts my niece and nephew so much they cry to me a lot and tell me why is she like this. When my sister is mad and she sees some small trash on the floor she will toss everything on the table to the floor. Scream and yell to pick it all up. When she's driving and she's upset with someone she will go over speed limit and drive out of the lane. Cars will honk. She'd cut people off. she does it for fun to be fun and faster. This is a text I got from my nephew one time when she was mad at him and driving.

I have 6 nieces and nephews in total. Oldest one is 17 youngest is 7. They tell me everything and anything that bothers them or they are questioning. My older sister is a good parent.

Through mom and dad's fighting. Brace yourself this is gonna be hard. My sister would belt them when they were lik 6 to 8. I would sleep over a lot so I'd get in the way telling her to stop They're just kids. They'll do it(clean their room) I thought it was normal cuz every parent did that but truthfully my parents never beat me because I didn't clean, in fact they never beat me at all. When I was 15 I'm 23 now. My sister would make fun of my body and call me names such as man boobs, fat girl, ugly, etc. She'd say this in front of my brother inlaw and he'd just look at me like what am I supposed to say? I'm sorry I don't know what to do. This happened for years. She bully and put me down. She'd get into fights with other women(verbal). She was a nice person before she met her ex husband I don't know what changed. He was never a mean person. Neither were our parents. What he did bring however was a lot money to the table. We grew up poor maybe this corrupted her. I love my sister I just can't do nothing. My neice mentioned she hit my nephew on thw shoulder and bruised him. One time i almost striked her because she kept getting into my personal space. I held back but she just kept at it. I immediately walked out of my moms house. I just didnt want any trouble or to hurt my niece or nephew by attacking their mom. So present day. I spoke to my niece about this while she cried with my older sister, my mom and her cousins around. My sister had no history of drugs. She just acts so stupid sometimes like she's a child. She will yell and scream and play the kids absolutely can't stand it. It's either her being this weird woman child or she will be the serious angry person who throws shit on the floor and curses them to die. They've both told me she curses them calling them little bitches, little mother fuckers. Your dad doesn't give me money. They started calling her gold digger. To keep them happy and sound I have started a weekly run to get food, dessert and go to the store so I can make sure they're emotionally ok. And so they can see their cousins. Their mom isn't allowed there because she fights with my brother inlaw older one and told him to go die. So she doesnt want her around. My she says things like I'll tie u up with ur lil dick to my nephew if he says anything back. Yesterday all he said mom you're not being a mom get off your phone. Why would you say this to your child who wants attention. So disgusting. For the record she would not get off her phone at all. After we all asked her to stop. My niece hates when anyone mentions any body parts or anything about sex or anything explicit due to my sister. My sister always touches they're body parts like when they were younger and you'd play but they said we are older we don't like that please stop but she I guess still does it after we talked about stopping that. Also she says things like if I had a man I would leave you guys. One time she overheard her father on the phone saying wait till they're 18 I want nothing to do with them they'll be your problem then. I know he was angry but damn that wasn't right to say under any context. When my nephew goes over to his house. He had access to his fathers car at his dad's house and a few months ago he took it for a joy ride 80 mph and he took it on the freeway. His dad is teaching him to drive. Qlso his dad did not discipline him for shit. He just scolded him. Their dad sometimes leaves them alone on the days they're with him on every other weekend. Or he takes them to his moms house. I understand he gets busy but if you get two weekends out of a month where the hell do you have to be if not with your kids. 4 days out of the month.

My niece feels like she can't rely on both of them because they probably eill just leave when it's convenient.

I love them so very dearly. I hate to see them in so much pain.

I asked my niece if she wants to live with her mom, me or her dad. She said I just don't wanna be there anymore. I told her I will fight for custody somehow of she wants to live with me. She said yes that would be very good. Well guys if anyone has any legal advice. Please do let me know. Thanks. For reference. I'm 23 from California. I work full-time. I also go to school. I live with roommates atm. Thanks :) my name Lori.